Volume 29 Nos 5-7 - Asian Journal of Physics

ASIAN JOURNAL OF PHYSICS

An International Peer Reviewed Research Journal
Frequency : Monthly,
ISSN : 0971 – 3093
Editor-In-Chief (Hon.) :
Dr. V.K. Rastogi
e-mail:[email protected]
[email protected]

AJP

ISSN : 0971 – 3093
Vol 29, Nos 5-7, May-July, 2020

Asian
Journal of Physics

Vol 29, Nos 5-7, May-July, 2020

A Special Issue Dedicated to Prof Robert R Alfano
Guest Edited By : Prof Asima Pradhan

Anita Publications
FF-43, 1st Floor, Mangal Bazar, Laxmi Nagar, Delhi-110 092, India

Robert R Alfano, Distinguished Professor of Science and Engineering at The City College of the City University of New York, has contributed significantly to the field of ultrafast laser science and is a pioneer in the application of light and photonics technologies to the study of biological, biomedical and condensed matter systems. Prof Alfano’s contributions to photonics have been tremendous, encompassing several key areas starting with semiconductor materials and devices, nonlinear optics, ultrafast lasers leading to discovery of new tunable lasers, nanotechnology, developments in coherent back scattering to initiating the field of biomedical spectroscopy and imaging. His intuitive scientific prowess has given rise to several original contributions in photonics research, new discoveries and novel instrumentation. His crowning research achievements include discovery of the supercontinuum, development of new tunable Cr3+/Cr4+ lasers, advances in laser spectroscopic and optical imaging techniques, and study of ultrafast optical pulse propagation and imaging in scattering media. His accidental discovery of the supercontinuum, 50 years ago, has far reaching consequences and has now found use in hospitals and medical units, in a range of applications in surgery and
treatment. Prof Alfano is the father of Biophotonics, pioneering the use of light for disease diagnostics and cure. Optical Coherence Tomography (OCT) which is now a commonly used imaging instrument found in most ophthalmology clinics, is based on white light supercontinuum source that he discovered. He has always worked in forefront areas, reflected by his recent work where he has launched the use of quantum entangled photons for brain imaging.
His pioneering work in 1981, using fluorescence spectroscopy to detect dental cavities, paved the path to non-invasive detection of cancer and ultimately created the vast research area of biomedical optics, known as biophotonics. He coined words like Optical Biopsy in the early days of his research in biomedical optics in his Institute for Ultrafast Lasers and Spectroscopy, and subsequently, snake-like photons while attempting to understand light propagation in turbid media such as biological tissue. The area of biophotonics, the use of light for biomedical applications, became a major research area of his newly formed center, Institute for Ultrafast Lasers and Spectroscopy (IUSL) in CCNY in 1982. Exciting trptophan, tyrosin and NADH through UV light and investigating their behavior in normal and cancer tissues threw new light in disease development and its progression. Several patents followed from these biomedical research led to inolved many laboratories in the world developing dedicated research groups to bio photonics. Prof Alfano credits most of his work on building optical devices to IUSL engineer, Yuri Budansky, whose magical hands helped bring ideas into physical reality.
Prof Alfano is a fellow of APS, OSA, IEEE, NY Academy of Sciences, and Alfred P Sloan fellow. He received his Ph D in Physics from New York University. He spent 8 years at GTE Labs (now Verizon) before joining CCNY. At CCNY, he founded the Institute for Ultrafast Lasers and Spectroscopy (IUSL), the first such centre to focus on ultrafast light, where he trained more than 50 doctoral students and mentored a similar number of post doctoral fellows, from physics and electrical engineering. The institute has also developed training programs to encourage students of middle schools to college for them to pursue science, technology and engineering as careers. He attracted significant funding to IUSL, competing against the best in the world. Prof Alfano has played a key role in developing the areas of Biophotonics by organizing topical meetings and conferences of SPIE and OSA. A Fellow of the American Physical Society, the Optical Society of America, the Institute of Electrical and Electronics Engineers, the New York Academy of Sciences, an Alfred P. Sloan Fellow, he has received the Coherent Biophotonics Lifetime Achievement Award, the Leonardo Da Vinci Award, the Lifetime Achievement Award of the Association of Italian American Educators. He has received several other prestigious awards, such as the OSA Charles Hard Townes Award in 2008, the first SPIE Britton Chance Biomedical Optics Award in 2012, APS Arthur L Schawlow Prize in Laser Science in 2013, OSA Michael Feld Award in Biophotonics in 2016 , and SPIE Gold Medal Award in 2019 . He has published over 750 papers and 128 patents and 41,218 citations with H –index 98. In the area of biomedical optics alone he holds over 45 patents and has published more than 250 articles.

Professor Robert Alfano (right) receiving the 2013 Schawiow Prize in Laser Science from Dr. Henry C, Kapteyn, Chair of the American Physical Society Division of Laser Science

Prof Alfano (left) in his office at IUSL, CCNY with IUSL engineer, Yuri Budansky and
Prof Asima Pradhan (centre) in 2014

Guest Editorial

When I was offered the task to guest edit a special issue of the Asian Journal of Physics, dedicated to Prof Robert R Alfano, by the Editor-in-Chief, Prof Vinod Rastogi, I gladly accepted it. It is indeed an honour to do this job, largely because Prof Alfano was my doctoral supervisor and then, because of his tremendous contributions to the area of photonics. Let me begin by writing about Prof Alfano, who, of course, needs no introduction in the photonics community.

Prof Alfano hailed from Teaneck, New Jersey from a family of Italian origin that believed in the transforming power of higher education. He went to the nearby T Dickinson University (TDU), planning to pursue electrical engineering. The boredom of tedious laboratory work pushed him towards physics, a subject requiring less laboratory hours. His natural liking of mathematics made him take a large number of mathematics courses, compensating for the liberal arts requirements. He excelled in physics and got a job in Sylvania, a part of General Telephone (GT), after his first rejection from a company that would become Verizon later. At GT, he met several researchers, who went on to have a lifelong influence on him, the prominent one being Stanley Shapiro, with whom he discovered the supercontinuum at GT and obtained his first patent in 1974, out of the 129 patents he has to his name till date. Professor Alfano and S Shapiro published their discovery of the broad emission between 400nm and 700nm in Physical Review Letter (PRL) and subsequently published a series of PRLs dealing with self phase modulation and four photon coupling in glass.

Prof Alfano is a pioneer in the applications of light and photonics technologies to the study of biological, biomedical and condensed matter systems. In the late 1970’s and early 80s, his research focus was on ultrafast laser pulses and production of picosecond pulses by mode-locking. His laboratory, which eventually became the Institute for Ultrafast Spectroscopy (IUSL), could boast of home-built picosecond Nd-Glass lasers, which, as graduate students, many of us handled in the 1980s. Schiller and Alfano studied the broadening of ultrafast pulses passing through a spectrograph using the super ultrafast temporal and spectral measuring tool, the streak camera. In fact, Alfano’s lab was literally “littered” with streak cameras at a time when it was almost unheard of in many labs.

The 1980s was the period when the IUSL was booming with activity. Alfano had already initiated his pioneering work in biomedical optics by developing the method and apparatus for detection of caries in teeth using luminescence in 1981. He held 14 patents in that decade with developments, ranging from methods to calibrate the streak camera, to developing picosecond gated light detection tube, to producing new Emerald Laser, Chromium Doped Beryllium Aluminum Silicate Laser Systems and in the area of biophotonics. The next decade of the 90’s began with the lasing action in Chromium-doped Forsterite, which brought in a new excitement in IUSL. The decade also established the era of biophotonics with patents on laser based cancer diagnosis. Prof Alfano became a pioneer in various domains of biophotonics. Use of fluorescence spectroscopy and lifetimes for cancer diagnosis, determining key wavelengths and signatures from native fluorophores, associated with tumor detection were his initiatives in the late 1980s and early 1990. The idea of utilising the property of specificity of Raman spectroscopy to distinguish the various types of atherosclerotic plaque was one of his initiatives. Subsequently, Raman signatures have been exploited as a biological diagnostic tool in the biomedical research arena. Analysing fluorescence spectroscopic data in biological tissue led to the understanding the effects of scattering and absorption. A series of path breaking research evolved, on imaging in random media and detection of hidden objects in highly scattering media, again initiated by Prof. Alfano. Synchronous fluorescence (Stokes shift spectroscopy or S3) is known to decouple overlapping fluorophores. Exploiting this for better diagnostics was a neat idea for complex systems like biological tissue. A natural offshoot of his seminal work on supercontinuum generation was to develop sources for techniques such as S3, which led to several patents. His pioneering work in 1981, using fluorescence spectroscopy to detect dental cavities, paved the path to non-invasive detection of cancer and ultimately created the vast research area of biomedical optics known as biophotonics. Optical Coherence Tomography, which is now a commonly used imaging instrument found in most ophthalmology clinics, is based on white light supercontinuum source that he discovered. Deep tissue imaging with multiphoton excitation, Resonance Raman based instrument, Stimulated Raman vibration microscope, spatial frequency spectrometer were all his patented ideas. His intuitive scientific prowess has given rise to several original contributions in photonics research, new discoveries and novel instrumentation. He has always worked in forefront areas, reflected by his recent work, where he has launched the use of quantum entangled photons for brain imaging. He coined words like ‘Optical Biopsy’ in the early days of his research in biomedical optics and subsequently, ‘snake-like photons’ while attempting to understand light propagation in turbid media. The area of biophotonics became a major research area of his Institute for Ultrafast Lasers and Spectroscopy in the City College of the City University of New York, since 1982. Prof. Alfano can well be known as the ‘father of biophotonics’, pioneering the use of light for disease diagnostics and cure.

It is thus an honour for me to dedicate this issue to Prof Robert R Alfano. After accepting the task of being the Guest Editor, my first thoughts for contributions to this special issue, were to invite ex-students and well wishers of Prof. Alfano. The goal of this issue then becomes a representation of his work through the research developments of students he trained or his well-wishers and subsequently, the next generation in the area of photonics. The issue contains 15 invited articles by experts in photonics, spanning areas such as Biophotonics, Supercontinuum light, 2D materials in photonics, fiber optics, Nonlinear optics, high intensity laser physics, nanophotonics and optical tomography. It essentially offers a glimpse of a large area of photonics, especially focussing on the research initiated by Prof. Alfano.

The issue begins with an article on quantum entanglement for tissue diagnosis. The phenomenon of quantum entanglement originated from the famous EPR paradox (1935), where the effect was thought to be impossible, thereby pointing towards incompleteness of the quantum theory. However, the validity of quantum mechanics has since been established through experiments with polarization or spin of entangled photons, measured at separate locations. Light matter interaction is generally treated classically or semi-classically. The last few decades have seen the emergence of the use of superposition of quantum states, primarily for the purpose of conveying information. This has led to the growth of a new interdisciplinary field of science technology, known as quantum information, which does not focus on the physical medium but on its quantum preparation and evolution. The question that one asks is then the following: can decoherence of entanglement of two photons be used for the purpose of medical diagnosis? Prof Enrique Galvez and co-authors have elaborated on this technique and how it can be applied to tissue diagnostics, a forefront research development. Their work showed that in passage through thin slices of tissue, entanglement seems quite robust against decoherence. A second ongoing effort investigates whether entanglement can distinguish between healthy or diseased brain tissue.

Enrique Galvez is professor at Colgate University, in Hamilton, New York, USA. His association with Prof Alfano has been for over 20 years. One of his students was a graduate student with Prof Alfano. In his words,

“in 2015 I spent a sabbatical at City College, which became the genesis of the project involving my submission, on using quantum entanglement to diagnose brain disease. Since then we have been research collaborators”.

An issue dedicated to Prof Alfano would be incomplete without an article on supercontinuum of light So the next article by Dr Lingyan Shi is a review on supercontinuum, which may interest readers, especially since it focuses on the applications of the supercontinuum source. Dr Lingyan pursued her postdoctoral research with Prof Alfano. In her words,

“It was such a fortunate event after I asked Dr Giovanni Milione a question about laser-tissue interaction, he took me to Prof Alfano’s office and told me: “This Professor is extremely knowledgeable and will give you a good explanation.” At that time, I was a second year Ph D student at City College of New York, where I had the opportunity to continue discussions with Prof Alfano’s on various optical imaging problems and later become a postdoc in his Lab to explore multiple biophotonics applications. I was lucky to have seen and experienced the diligent and creative daily research activities at IUSL under Prof Alfano’s leadership. His vision and insightfulness, and the environment he created made it possible for all of us who worked under him to ‘go beyond’ and ‘dig deep’. He gave every one of us the opportunity and “led us to water”, and using his own words: “You drink it!” He highly impacted on my career path in academia. His curiosity, passion, creativity, and hard-working will always positively influence us and encourage us to explore and go beyond.”

Biophotonics research in Prof. Alfano’s laboratory began as a hobby and a high school project of his daughter. However, in the next 20 to 30 years, it became the major research area of IUSL. Thus it is not surprising that in this issue one third of the articles deal with light based research on biological systems. The first article on Biophotonics deals with fluorescence spectroscopy for solid tumor detection. As mentioned earlier, Prof. Alfano and his group have worked extensively on tissue diagnostics, using fluorescence, Raman and elastic scattering techniques. This paved the way for biophotonics research in diagnostics of various diseases. Fluorescence spectroscopy, due to its sensitivity, is a preferred tool utilised by several researchers. In the very early phase of this work, the focus was on determining the dominant native fluorophores and the key excitation wavelengths for diagnosis. Over the past 30 years the research has moved towards developing novel techniques for early diagnosis, instrument designing and fabrication for clinical testing and development of classification algorithms. However, the precision of diagnosis is still an area which is quite important and the article by Laura Sordillo and Peter Sordillo deals with determining the aggressiveness of solid tumors of the breast by correlating with the contributing native fluorophores. The study is performed using a portable, miniature, easy to use UV LED ratiometer unit, built in Prof Alfano’s lab. Laura Sordillo was a graduate student of Prof Alfano is continuing as a Research Assistant Professor at the Institute for Ultrafast Spectroscopy and Lasers. She published many important papers with Professor Alfano, including the use of the short wavelength infrared (SWIR) windows for biomedical applications (including the brain, cancerous tissue and bone fractures). They are now investigating the existence of quantum effects in photosynthesis and in the human brain using ultrafast light techniques.

An offshoot of fluorescence spectroscopy is the Stokes Shift Spectroscopy (S3) or synchronous fluorescence spectroscopy, where, if an offset between the excitation and emission wavelengths matches the difference between the absorption and fluorescence peaks of a certain fluorophore, it produces a sharp peak. This brilliant technique, introduced in 1971 helps decouple contributing fluorophores in a multicomponent system, making it both a specific and a sensitive tool. Prof. Alfano was again instrumental in bringing this method to the forefront for understanding complex tissue fluorescence in disease development. Interestingly, this issue contains three articles dealing with synchronous fluorescence, displaying the recent applications of S3 in biophotonics and nanophotonics. One such novel study is by Prof Masilamani, in using this technique to test the presence of purity of a quantum dot of a certain size by ascertaining the presence or absence of a quantum dot of a different size whose signature spectrum shows up in the synchronous spectrum. Prof Masilamani has just retired as distinguished professor from King Saud University, Riyadh KSA. He had been following Prof Alfano’s work since 1980, when he was a graduate student at IIT Madras, India. In his words,

“I was fascinated and longing to work with him for a long time and finally, I had the opportunity to spend three months in his Lab in New York on time-resolved spectra of benign and malignant prostate tissue. All through the time, he was very cordial, friendly and easy to access. He had a soft corner for all those coming from developing countries and who were able to access the very modern advanced facilities because of his broad mind. For me, he is a fine scientist and a cultured gentleman. I have cherished memories of New York because of him.”

The next article is a short review on 2D semiconductors, which are increasingly becoming important in photonic applications as optical or optoelectronic devices. Over the past decade, graphene has been extensively studied as a 2D material for such devices. Currently, transition metal dichalcogenides (TMDs) are being investigated for 2D semiconductor based optoelectronic devices due to their remarkable linear and nonlinear properties. Nanophotonics based investigations, to understand the strong light matter interactions in such materials, is the focus of this review by Prof Vinod Menon. Prof Menon joined CUNY as part of the Photonics Cluster hires that was initiated through the vision of Prof Alfano back in 2004. In his words

“In my early days as an assistant professor, I greatly enjoyed the photonics meet ups he organized and the support he provided to junior faculty – and I was one of them. Prof. Alfano has played a key role in putting CUNY on the photonics world map and this is another aspect that has benefited all of us in the field at CUNY. Finally, as a colleague and collaborator, he is great to work with and is always bubbling with new ideas. I consider myself lucky to have a colleague like him at CCNY!”

The next article is again based on supercontinuum, dealing with one of the processes responsible for its generation, self phase modulation (SPM). As mentioned earlier, supercontinuum generation has been investigated in various nonlinear media and seen to be better controlled in optical fibers. Wider spectral broadening of SPM in optical fibers can be generated using picosecond laser pulses. The fine structures observed in the wide SPM spectra have garnered a lot of interest. In this study, the authors, Dr Q Z Wang and Prof P P Ho reviewed the theoretical and experimental measurements of SPM spectra generated with picosecond laser pulses propagating in optical fibers. Both authors have worked for several years with Prof. Alfano, Dr. Wang as a graduate student and Prof. Ho as a collaborating researcher in IUSL.

Another of Prof. Alfano’s 57 Ph.D students, Dr B B Das, who has contributed to the Biophotonics research from its infancy has written a short review on the applications of nonlinear processes in biological systems. In the article, he has provided a flavour of second harmonic generation and other multiphoton processes in imaging of biological tissue, beginning with an introduction to the basics of nonlinear processes. Having been closely associated with Prof Alfano for over 25 years, he is an ideal candidate for writing about his contribution to nonlinear processes in biophotonics. Dr Das has provided lively descriptions of the work at IUSL on SHG imaging in cancer detection, two-photon excitation imaging of tryptophan distribution and an interesting study on Alzheimer’s disease time resolved fluorescence using multi-photon excitation. Combining these two powerful techniques, Dr Das compared the decay times of one and two photon processes to understand the underlying physical phenomenon. With his long association with Prof Alfano, Dr Das writes,

“Professor Alfano has a child-like curiosity about various scientific problems with a matching tenacity to pursue it incessantly once he makes up his mind. Whenever I send him a manuscript around midnight the reply with corrections would be back before early morning. Many times I wondered if he slept at all. I have never seen him saying no to an undergraduate student looking for research experience in his lab. He is an institution at CCNY.”

The subsequent articles were by researchers who have done forefront work in photonics and others who are ‘the second generation products’ of Alfano!

Prof Ravindra Kumar needs no introduction to the photonics community, having contributed enormously in the area of high intensity laser matter interactions which create plasmas of mega ampere currents in the laboratory. Such plasmas generate the highest terrestrially available magnetic fields. Studying the mega gauss magnetic fields helps understand the complex physics involved in ultrafast light and the electron transport properties inside the plasma. Prof. Ravindra Kumar and his team have used two-colour, pump-probe reflectivity and Doppler spectrometry on the critical surface of hot, dense laser produced plasma to understand its rapid motion and generation of shock waves. Crucial information is gathered from the temporal studies of the mega gauss magnetic fields, comparing such results with measurements using low contrast pulse. A final note by the authors on generation of an efficient supercontinuum laser probe is to obtain information of the critical density surface at various depths that shows the influence of Prof. Alfano’s seminal work in various applications. Prof Ravindra Kumar mentions,

“I never met Prof Alfano in person either in India or abroad, but to me the influence of his work in many areas of NLO was evident once I started working for a Ph D. His work on supercontinuum was of course path breaking and spectacular but I came across his papers in other areas of nonlinear optics too and was grateful to learn from those. My actual areas of research did not overlap with his but in my teaching his work was very useful.”

An issue on photonics would be incomplete without an article on photonic crystals which are extensively studied due to their amazing property of being able to control light. An illuminating article by Prof. H.Wanare, describes how light flow is controlled by weak perturbations by adding a very small dielectric rod or impinging a femtosecond pulse, which alter the refractive index locally. Weak perturbations are compared with strong ones and various spatial modes are studied through numerical simulations using the finite difference time domain tools. Prof Wanare has been greatly influenced by Prof Alfano’s work during his graduate and postgraduate days and in his words,

“His pioneering studies on time-resolved imaging in random media were extremely exciting to us. These studies attracted us immensely as we were developing then (late 1990s) the split-operator technique to solve Maxwell’s equation is exactly in random media. It was inspirational to test for ourselves the validity of the diffusion approximation that he had talked about in the early 1990s.”

Globally, a significant amount of time has been invested in nanophotonics due to its long term implications in revolutionizing technology. Fabrication of nanoparticles and other nanostructures is thus an area of great interest. Prof. Narayan Rao’s article in this issue deals with nanostructure fabrication, specifically Laser Induced Periodic Surface Structures. Fabrication is done on different metals, using a simple and single step experimental technique of Laser Direct Writing (LDW). An analysis based on the decay lengths of surface Plasmon polaritons is performed to find out which metals can be potential candidates as perfect absorbers by suppression of total and specular reflections over a large wavelength regime.

The next 5 articles are devoted to Biophotonics, an area that Prof Alfano has pioneered since early 1980s and still continues to bring in novel ideas to the domain with his keen insight. The ‘next generation’ Biophotonics researchers are also working on innovative ideas as can be seen in the next article by Dr Nrusingha Biswal. His team has worked on a neat idea of utilising the imperfections in optical filters to extract the absolute phase lag maps of biological tissue in frequency domain measurements. This has led to improvements in radiative transport model based reconstructions.

Use of nanoparticles in biomedical applications, majorly in sensing and drug delivery, is a well established area of research. Dr Sharad Gupta’s article here discusses a simple chemical technique of synthesizing ZnO nanoparticles using tulsi (holy basil) extract as a reducing and stabilizing agent. This green chemistry technique was found to produce pure, crystalline, spherical nanoparticles, with uniform size distribution and biocompatibility.

An area extensively researched is noninvasive disease diagnostics through optical spectroscopy. Over the last 35 years, studies have been conducted on human tissue, on different organs in patients to detect signatures of the disease. However, very little attention has been given to body fluids, which can reflect similar changes as in tissues and yet be completely noninvasive. Two of the next few articles focus on this aspect. The article by Prof. Ganesan investigates through fluorescence and excitation spectra, the efficacy of blood plasma as a diagnostic medium for detection of different stages of cervical cancer. A statistical analysis based on linear discriminant analysis showed that blood plasma is a potential candidate as a diagnostic medium.

The fourth article on tissue diagnostics by Dr Ebenezer Jeyasingh uses synchronous fluorescence spectroscopy (SFS) to examine early tissue transformation in DMBA treated mouse skin carcinogenesis models. With a ratio mapping algorithm, the study indicates that early transformations can be detected by SFS.

The final article by Pavan Kumar and Asima Pradhan exploits the specific nature of SFS in probing another body fluid, saliva for early developments of oral cancer. The efficacy of saliva as a diagnostic medium is displayed by comparing the results with those of oral tissue SFS.

As can be seen now, the fifteen articles provide a flavour of the various fields in photonics and laser matter interaction.

I am particularly pleased and grateful to have the foreword written by Peter Delfeyett, Pegasus Professor and Trustee Chair Professor of Optics, EE & Physics in CREOL, The College of Optics and Photonics, University of Central Florida who is currently serving as the Director of the Townes Laser Institute. Peter was a graduate student at IUSL and so it is appropriate for someone who has had a long association with Prof. Alfano to write the foreword.

I am also extremely grateful to Prof G P Agrawal, James C Wyant Professor of Optics of the Institute of Optics at University of Rochester, NY, USA and Prof Arjun Yodh. James M Skinner Professor of Science at the University of Pennsylvania (Penn) and the Director of Penn’s Laboratory for Research on the Structure of Matter (LRSM) and its NSF-Supported Materials Science and Engineering Center (MRSEC), for sparing valuable time from their other commitments (due to which they could not contribute articles) to write two pleasant letters of appreciation on their association with Prof Alfano.

I would also like to thank all the authors and co-authors for their efforts in making this special issue possible. I am indebted to them, more so because of the terrible times we are in this year. They could manage to write articles in State of the Art subjects in photonics, which will surely interest readers, especially during a period when students and staff could assist only remotely. I am quite certain that readers will benefit from these insightful articles.

Finally, I would like to thank the editorial team for their tremendous efforts during this period. I am grateful to Er Manoj, Ms A Singh and Ms. Laxmi for their tireless work, day in, day out. Last but not the least, a big thanks to Prof Vinod Rastogi for being a pillar of support in this debut editorial venture of mine.

Asima Pradhan

About Guest Editors

Prof Asima Pradhan completed her M Sc from Delhi University and carried out her Ph D under supervision of Prof R R Alfano at City University New York. During her doctoral studies, she was involved in the pioneering auto-fluorescence spectroscopic studies on tissue and its application for diagnosis of cancer. She joined Department of Physics, IIT Kanpur in 1993 and was also associated with the Centre for Lasers and Photonics at IIT Kanpur. Prof Pradhan’s research interests have been in the area of Biophotonics, attempting to understand tissue fluorescence in human tissue environment and to evaluate its use for early diagnosis of disease. She has more than 100 publications and two patents to her credit. Her current interests are to explore ways to improve diagnostic capabilities of the fluorescence-based approach in order take it towards the desired goal of non-invasive and early detection of disease, specifically cancer. She has a long-term collaboration with GSVM medical college, Kanpur and more recently, with AIIMS Bhubaneswar. She, along with her group, has investigated fluorescence spectroscopy, imaging and statistical analysis techniques to study progression of cervical, oral and breast cancer. Her group developed and validated a novel method for extraction of intrinsic fluorescence using polarized fluorescence and elastic scattering spectra. The technique was subsequently applied for diagnosis of cervical cancer. A hand held polarized fluorescence based probe was designed, fabricated and calibrated by her group. Currently, the probe is under testing for in-vivo application at GSVM medical college and AIIMS Bhubaneswar. Based on this work, her student and the entire team were granted the Gandhian Young Technological Innovation (GYTI) Award in 2016 during the Festival of Innovation, at Rastrapati Bhawan, Delhi. Her work on device development has culminated in a startup to design and fabricate smartphone based prototype device for cervical cancer detection.

Prof Alfano (left) and Prof Asima Pradhan

Appreciation

Diffuse Reflections on Bob Alfano

I never worked with Bob Alfano, but our paths overlapped in interesting ways, and I have come to appreciate Bob from a different perspective than that of a mentee, collaborator, or university colleague. I hope this perspective will interest the reader. In a few words, Bob is smart, fast-working, confident, competitive, outgoing, argumentative, and fun. In this rumination, I will not provide a document that extols and details Bob’s accomplishments; I have done this before! Rather, I will attempt to present a “diffuse” image of Bob based on our varied connections over the years. In many ways, this reflection is an accounting of Bob’s influence on my own growth as a participant in the scientific enterprise.
My Ph D and post-doc research centered on atomic and optical physics at Harvard and AT&T Bell Labs. Therefore, my scientific “family” was different from Bob’s. But we used lasers, and early-on I was aware of good things happening in Bob’s lab, especially in ultrafast optics. His pioneering work on self-phase modulation was truly important. It laid the basis for continuum generation and continuum light sources. At the time, I did not think Bob got enough credit for this contribution, but thankfully he is recognized for it now. Over the years, I also connected with a few of Bob’s mentees from these earlier days (e.g., Tony Johnson, Peter Delfyett, Asima Pradhan). They were expertly trained and successful. They were happy about their early research experiences, and they were fond of Bob. In my view, that’s exactly what an advisor hopes for, and success in this regard says something very positive about Bob.
Bob and I “intersected” more directly in the early 1990s, when I was an Assistant Professor at the University of Pennsylvania. One of Bob’s projects came onto my radar because it involved collaboration with Lewis Rothberg. Lewis was a good friend from graduate school, and as far as I was concerned, just the fact that Lewis was collaborating with Bob was a point in Bob’s favor. Their experiment aimed for nothing less than to understand the first steps of vision. To this end, they carried out a beautiful time-resolved absorption measurement of the bovine visual pigment rhodopsin, which was published in PNAS. At Lewis’s suggestion, I attended a talk about the paper at a major optics conference. The talk was excellent, the data was clean, and the interpretation of the data was logical. Thus I was stunned when the audience reacted in a hostile way during the question period. The hostility stemmed from data interpretation. Ultimately, measurements with better temporal-resolution would be needed, but Bob’s data was State-of-the-Art at the time, and the analysis, while not the only possible explanation, was straightforward and sensible. For this reason, I could not understand the crowd reaction. Most interesting for me, however, was not the crowd hostility. Rather, I was intrigued with how Bob engaged with the audience. He seemed to enjoy the intensity in the room; he seemed to thrive on it. He managed it. That’s Bob.
My second major encounter with Bob was closer to home and in the same time-frame. At Penn, my research in diffuse optics was going full-force, and I had cultivated a terrific collaboration with Britton Chance to push our ideas into the clinic. Britt was a biophysicist of the highest caliber who dug deep into the biology, and who consistently translated the “latest” technologies into the clinic; as I understand, Britt inspired Bob to move into Biophotonics. At any rate, Bob had published a paper in Science (and follow-up papers) about visualizing turbid media like tissue with ballistic photons, and Bob was lobbying hard in the Biomedical Optics community to apply this concept for breast cancer imaging. I pushed back. So did others in the community. I was a pioneering devotee of the diffusion approach. I had experimented with gating too, in a different context, and while I felt that Bob had an interesting idea, the breast imaging problem was not the right one for the technology – too much tissue scattering. We were competitors for intellectual and financial resources within the same community, and the SPIE and OSA meetings were intense. Regardless, Bob exhibited scientific integrity under fire, and his efforts and exhortations brought out the best in us. One unanticipated positive consequence, for me, was that the subgroup that practiced diffusive tissue optics became more collegial, unified, and grew in number during this time. Through all of this, I respected Bob, and I sensed that Bob respected me. This is how science should work. Biomedical Optics marched forward.
The ballistic photon concept didn’t catch on for breast cancer imaging, but Bob’s ideas and related technology eventually found its way to other applications. Bob soon returned to problems that built on his earlier, excellent work exploring the potential of fluorescence and Raman spectroscopy for characterization and differentiation of diseased tissue. Bob, of course, continued to float new ideas and make interesting suggestions. One of his ideas that I recall, which perhaps was never published, was that we should push our whole enterprise from the near infrared (NIR) to the infrared (IR); tissue scattering and absorption are different in the IR and offer new contrast and potentially better signal-to-noise. This idea is trending now!
Besides research, Bob was an expert conference organizer. Bob was a “creation operator” for conferences. He started the OSA Biomedical Optics Topical Meeting in Florida. The creation of this conference was a very important contribution to our field. I attended all of these meetings and was a meeting Chair in the distant past. Our students and post-docs presented talks and posters at these meetings too (and they still present!). This particular meeting helped build our community. Bob is very proud of this contribution – he should be. Bob also organized a voluminous number of SPIE meetings, many with Britt, which were important as well, in part because they attracted a different mix of scientists and engineers to our subfield. These types of community building contributions, whose value is often underestimated, are vital for the field; success depends on the judgement and even-handedness of leaders like Bob.
Last year I gave the physics colloquium at CCNY. During the day and later at dinner, I had the great pleasure to meet again with Bob on his own turf. He was the same fast-moving “force of nature” I remembered, full of interesting ideas for experiments and full of stories. I had fun! I was well acquainted with Bob’s publications, but I had only a vague idea about his patents. Thus, a whole new (impressive) dimension in Bob’s career was revealed to me. I also learned about CCNY in its earlier years, and the role Bob played recruiting faculty and administrators and nurturing its science community. By the end of the evening, I felt energized to think about new problems and to try out new ideas in my lab! I am looking forward to our next encounter.

Arjun G Yodh is the James M Skinner Professor of Science at the University of Pennsylvania (Penn) and the Director of Penn’s Laboratory for Research on the Structure of Matter (LRSM) and its NSF-Supported Materials Science and Engineering Center (MRSEC). His home department is Physics and Astronomy. He is a member of the graduate groups of the Departments of Bioengineering and Materials Science & Engineering, and he is an active collaborator within the departments of Radiation Oncology and Radiology in the Perelman School of Medicine. Yodh’s research has spanned a wide range of fundamental and applied investigations in medical physics, biophysics, optical science, and condensed matter physics. This work includes pioneering work in biomedical optics wherein he has demonstrated and clinically translated concepts in light diffusion for noninvasive imaging and monitoring of tissue blood flow, hemodynamics, metabolic responses, and therapeutics in cancer and brain. His condensed matter research has ranged from nonlinear optics of solid-solid interfaces to fundamental research of soft matter; the latter includes studies of melting and frustration in colloids and liquid crystals, design and measurement of entropic forces, stabilization of carbon nanotubes in solution, and discoveries about the role of particle anisotropy in phenomena ranging from Brownian motion to coffee rings. Yodh has mentored ~100 Ph D students and post-doctoral associates during his career, while publishing ~350 papers (cited ~40,000 times, h-index, 108). Yodh has also made significant contributions to education, outreach and diversity at Penn as a program leader of a PREM partnership with the University of Puerto Rico, and as program leader of research experience programs at Penn for undergraduates (REU), high school students (PSSI), and high school teachers (RET). Yodh graduated from Cornell University (1981) with a B Sc in Applied & Engineering Physics; he obtained his Ph D from Harvard (1986) under the guidance of Tom Mossberg, and he then spent two years at AT&T Bell Laboratories as a post-doc working with Steven Chu and Harry Tom. Yodh joined the faculty at Penn in 1988, where he has remained for his entire career.

It’s an honor for me to write the forward for this Special Issue of the Asian Journal of Physics, in honor of Professor Robert R Alfano. Professor Alfano, in his more than 5 decades of his scientific contributions, has made many pioneering and seminal contributions to the areas of optical physics, ultrafast phenomena and spectroscopy, nonlinear optics, material science, imaging, biological sciences, and photonic devices.

His discoveries, such as the white-light supercontinuum, first generated 50 years ago, by the propagation of intense ultrashort optical pulses in matter, has led to breakthroughs in optical imaging using low-coherence tomography, and enabled the development of the stabilized optical frequency comb, for which the 2005 Nobel Prize in physics was awarded. At the same time of the discovery of supercontinuum, Prof Alfano was also the first to directly measure and time-resolve the ultrafast lifetime of optical phonons and study their decay to daughter phonons through anharmonic phonon-phonon interactions.

Even in his early days of measuring the dynamics of ultrafast optical interactions in condensed matter, he has been involved in pioneering applications of photonics to the area of biological sciences, and his efforts have led to what is now commonly called the “optical biopsy”, where light scattered from tissue could be used to determine whether the tissue was cancerous, with high sensitivity and specificity over 90%.

His expertise in ultrafast optical techniques in time-resolved spectroscopy led him to explore the fundamental nature of light scattering in highly scattering media, where he developed the concept of ballistic, snake-like, and diffusive photons, based on their time of flight within the media. He identified the ballistic and snake photons as carriers of information for direct shadow- gram imaging, which led to the development of various temporal gating techniques for direct two-dimensional imaging of inhomogeneities in random scattering media and biomedical samples.

Professor Alfano also opened the door to a new class of solid-state lasers based on his discovery of the Cr⁴⁺ ion as an active site for lasing, enabling ultrawide gain bandwidth and tunability in the infrared. These materials may one day become key in heterogeneous photonic integrated circuit platforms.

My point of this forward is not to enumerate all the wonderful and exciting discoveries made by Professor Alfano – there would not be enough space to properly detail those even if I were to use the entire space of this Special Issue. However, I would like to share a few of my close, personal connections with him. I met Prof Alfano as an undergraduate EE student in his optical physics class. At the end of each lecture, he would spend a few moments talking about his research. One day, he invited me into one of his labs, and when the laser fired, he said “Did you see that? Did you see the light? That was a picosecond!” Not only did I literally see the light, I figuratively ‘saw the light’ and at that moment, I was so inspired that I decided that I wanted a career in ultrafast science and technology.

After several years and a series of fortunate events, I became a Ph D student in his group, where I had the opportunity to continue in Prof Alfano’s footsteps and revisit optical phonon decay dynamics using a new ‘real time’ streak camera method we developed by exploiting the supercontinuum as a pump in a novel optical phase conjugation geometry. During my time as his graduate student, I was fortunate to have seen the development and evolution of several of his key discoveries. His vision and insightfulness, and the environment he created made it possible for all of us who worked under him to ‘go beyond’ and ‘dig deep’. He truly had a major impact on my career, and the careers of all of us that worked under him. He was more than our PhD or post-doc advisor; he was more of a true dad and coach. His excitement and creativity continue to inspire me to this day.

I’d also like to add that while I was in his group, there were many life lessons I learned. Prof Alfano would have several expressions that have lived with me since, such as “Listen with your good ear”, which over my career I have interpreted to mean to listen with openness and consider the possibilities. Another is “Don’t buy the yellow rug” which taught me to carefully consider what is practical and beneficial over the long run as compared to the short-term benefit. Another saying that is particularly fond for me is “It’s easy for those who see the light”. While doing science is challenging, I definitely saw the light the day I met Prof. Alfano.

Over his career, Prof Alfano has ~42,000 citations, >125 patents, >50 PhD students and > 50 post-doctoral fellows, and h-index of nearly 100, and these metrics are still not a good measure of his impact. I hope this forward gives the reader a glimpse of the rich range of subject matter and topics to which Prof Alfano has created. As you read the articles in this special issue, I hope you garner a true appreciation of the breadth and depth of his contributions. Perhaps you may even be stimulated to probe deeper into the references within these articles that cite his contributions so you can sense the expansive bandwidth of his contributions. I hope his contributions will inspire you as they have, and continue to do, for me.

Peter J Delfyett, Ph D

Pegasus Professor and Trustee Chair Professor of Optics, EE & Physics

Director, Townes Laser Institute,CREOL, The College of Optics & Photonics,

University of Central Florida

Prof. Alfano and Peter Delfyett, having lunch after Delfyett’s PhD defense.

My friendship and collaboration with Prof Alfano

Govind P Agrawal

The Institute of Optics, University of Rochester

[email protected]

I first met Prof Alfano in January 1977, soon after I joined the City College of City University of New York to work as a Postdoctoral Fellow under the supervision of Prof Melvin Lax. I heard about the Ultrafast Laboratory that Prof Alfano had setup there, and he was kind enough to allow me to visit it. Even tough I did not have a chance to collaborate with him, or his students, during the three years I spent at the City College, I was impressed with the research being carried out in Prof Alfano’s laboratory.

Fortunately, I had an opportunity to collaborate with Prof Alfano ten years later. I left City College to join AT&T Bell Laboratories in Murray Hill, NJ. Although, my work was initially related to the development of semiconductor lasers for telecom applications, after 1985 I became interested in studying the nonlinear effects taking place inside optical fibers. In 1987, I published a paper in Physical Review Letters with the title “Modulation instability induced by cross-phase modulation” that attracted considerable attention [1]. It so happened that Prof Alfano was also interested in the nonlinear phenomenon of cross-phase modulation. A French student, Patrice Baldeck, in his group was doing experiments in which ultrashort pulses were sent through optical fibers. I made a trip to the City College to meet Prof Alfano and Patrice, and we started a collaboration that turned out to be not only mutually beneficial but also quite fruitful. After presenting our work on “Generation of sub-100-fs pulses at 532 nm from modulation instability induced by cross-phase modulation in optical fibers” at the International conference Ultrafast Phenomena VI [2], we published our first joint paper in the June 1988 issue of Applied Physics Letters [3] under the title “Induced-frequency shift of copropagating ultrashort optical pulses.”

In our experiment, 25-ps pulses at 532 nm were propagated through an optical fiber together with intense 33-ps pulses at 1064 nm with an adjustable initial delay between the two pulses. The overlap of the two pulses resulted in a spectral shift of the green pulses through the cross-phase modulation induced on the green pulse by the intense pump pulse. The magnitude and the nature of the spectral shift (red versus blue shift) depended on the initial delay between the two pulses. A theoretical model based on the Kerr nonlinearity explained our experimental observations quite well. During the year 1989, we published three more joint papers, a remarkable accomplishment for any scientific collaboration [4-6].

My successful collaboration with Prof. Alfano during the years 1987 and 1988 resulted in a friendship that has continued to this day. I moved to University of Rochester in January 1989 to join the faculty of the Institute of Optics. When Prof. Alfano learned of my move, he asked me to visit him to give a research seminar at the City College. During our conversations, he indicated that everyone would be very happy if I were willing to accept a faculty position there. I felt honored but was not willing to move so quickly from Rochester, a place I liked, and thought would be best for my family. Prof. Alfano understood my situation and we remained good friends.He asked me to contribute a chapter to the book “Supercontiuuum Sources” that he edited in 1989. In 2016, he asked me to revise this chapter for the third edition of his book [7]. Prof. Alfano organized a special session on “45 years of supercontinuum generation” during the SPIE Photonics West Conference held in San Francisco, on, February 5, 2014. At his request, I gave an invited talk during this session [8] on the topic of “Supercontinuum generation in optical fibers and its biomedicalapplications.”

I am glad that I was provided an opportunity to contribute to the special issue of Asian Journal of Physics, published to celebrate the 50th anniversary of the discovery ofsupercontinuum generation by Alfano and his colleagues. I am fortunate to have collaborated with Prof. Alfano in the past and I value his friendship enormously.

References

Agrawal G P, Modulation instability induced by cross-phase modulation, Phys Rev Lett, 59(1987)880-883.
Baldeck P L, Alfano R R, Agrawal G P, Generation of sub-100-fs pulses at 532 nm from modulation instability induced by cross-phase modulation in optical fibers, Ultrafast Phenomena VI, (eds), by Yajima T, Yoshihara K, Harris C B, Shionoya S, (Springer), 1988, pp 53-55.
Baldeck P L, Alfano R R, Agrawal G P, Induced-frequency shift of copropagating ultrashort optical pulses, Appl Phys Lett, 52(1988)1939-1941.
Agrawal G P, Baldeck P L, Alfano R R, Optical wave breaking due to cross-phase modulation in optical fibers, Opt Lett, 14(1989)137-139.
Agrawal G P, Baldeck P L, Ho P P, Agrawal G P, Cross-phase modulation and induced focusing due to optical nonlinearities in optical fibers and bulk materials, J Opt Soc Am B, 6(1989)824-829.
Agrawal G P, Baldeck P L, Alfano R R, Modulation instability induced by cross-phase modulation in optical fibers, Phys Rev A, 39(1989)3406-3413.
Agrawal G P, Ultrashort pulse propagation in nonlineardispersive fibers, in The Supercontinuum Laser Source, (ed) Alfano R R, (Springer), 3rd edn, Chap 3, 2016.
Agrawal G P, Supercontinuum generation in optical fibers and its biomedical applications, in special session on 45 years of supercontinuum generation, Paper 894034, SPIE Photonics West, San Francisco, CA, 2014.

Govind P Agrawal

Prof Govind P. Agrawal is an expert on nonlinear optics, silicon photonics, and optical communications. He received the M. S. and Ph.D. degrees from the Indian Institute of Technology, New Delhi in 1971 and 1974 respectively. After holding positions at the Ecole Polytechnique, France, the City University of New York, and AT&T Bell Laboratories, Dr. Agrawal joined in 1989 the faculty of the Institute of Optics at University of Rochester, where he is currently James C. Wyant Professor of Optics. He is an author or coauthor of more than 450 research papers, and eight books. His books on Nonlinear Fiber Optics (Academic Press, 6th ed., 2019) and Fiber-Optic Communication Systems (Wiley, 5th edn., 2010) are used worldwide for research and teaching. From January 2014 to December 2019, Agrawal served as the Editor-in-Chief of the OSA journal Advances in Optics and Photonics.

Prof Agrawal is a Fellow of IEEE and OSA (The Optical society) and a Life Fellow of the Optical Society of India. He I also a member of Eurpean Physical Society. In 2012, IEEE Photonics Society honored him with its Quantum Electronics Award. He received in 2013 Riker University Award for Excellence in Graduate Teaching. Agrawal was given the Esther Hoffman Beller Medal in 2015.He was the recipient of two major awards in 2019: Max Born Award of the Optical Society and Quantum Electronics Prize of the European Physics Society.

Vol. 29 Nos 5-7, 2020, 379-386

Transmission quantum state tomography of biological tissue

E J Galvez¹,B Sharma¹, F K Williams¹, B Khajavi¹, and L Shi²

¹Department of Physics and Astronomy, Colgate University, Hamilton, NY 13346, USA

²Department of Bioengineering, University of California San Diego, La Jolla, CA-92093, USA

³Insititute for Ultrafast Spectroscopy and Lasers, City College of New York, NY-10031, USA

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

We present a new type of measurement based on quantum entanglement of photon pairs for use in diagnosing tissue. As polarization-entangled photons traverse through an organic tissue, multiple scattering events incrementally decohere the state of the light, reducing the entanglement. We use quantum metrics that evaluate the state of the light as a means to infer structural differences between different types of tissues. © Anita Publications. All rights reserved.

Keywords: Quantum state tomography, Entangled photons, Biological tissue diagnosis

References

1. Alfano R R, Shi L, Neurophotonics and Biomedical Spectroscopy, (Elsevier, Radarweg), 2018.

2. Fujimoto J D, Farkas D L, (eds), Biomedical Optical Imaging, (Oxford University Press, Oxford), 2009.

3. Mandel L, Wolf E, Optical Coherence and Quantum Optics, (Cambridge University Press, Cambridge), 2007.

4. Feynman, R P, Leighton R B, Sands M, Lectures in Physics, Vol 3, (Addison-Wessley, Reading), 1968.

5. Nielsen M A, Chuang I L, Quantum Computation and Quantum Information, (Cambridge University Press, Cambridge), 2007.

6. Aspect A, Grangier P, Roger G, Experimental Realization of Einstein-Podolsky-Rosen-Bohm Gedanken experiment: A New Violation of Bell’s Inequalities, Phys Rev Lett, 49(1982)91-94.

7. Giustina M, Mech A, Ramelow S, Wittmann B, Kofler J, Beyer J, Lita A, Calkins B, Gerrits T, Nam S W, Ursin R, Zeilinger A, Bell violation using entangled photons without the fair-sampling assumption, Nature, 497(2015)227-230.

8. Shalm L K, Meyer-Scott E, Christensen B G, Bierhorst P, Wayne M A, Stevens M J, Gerrits T, Glancy S, Hame D R, Allman M S, Coakley K J, Dyer S D, Hodge C, Lita A E, Verma V B, Lambrocco C, Tortorici E, Migdall A L, Zhang Y, Kumor D R, Farr W H, Marsili F, Shaw M D, Stern J A, Abellán C, Amaya W, Pruneri V, Jennewein T, Mitchell M W, Kwiat P G, Bienfang J C, Mirin R P, Knill E, Nam S W, Strong loophole-free rest of local Realism, Phys Rev Lett, 115(2015)250402; doi.org/10.1103/PhysRevLett.115.250402.

9. Shi L, Galvez E J, Alfano R R, Photon Entanglement Through Brain Tissue, Sci Rep, 6(2016)37714; doi.org/10.1038/srep37714.

10. Kwiat, P G, Waks E, White A G, Appelbaum I, Eberhard P H, Ultrabright source of polarization-entangled photons, Phys Rev A, 60(1999)R773-R776.

11. Dehlinger D, Mitchell M, Entangled photons, nonlocality, and Bell inequalities in the undergraduate laboratory, Am J Phys, 70(2002)903; doi.org/10.1119/1.1498860.

12. Rangarajan R, Goggin M, Kwiat P, Optimizing type-I polarization-entangled photons, Opt Express, 17(2009)18920-18933.

13. James D F V, Kwiat P G, Munro W J, White A G, On the Measurement of qubits, Asymptotic Theory of Quantum Statistical Inference, (2005)509-538; doi.org/10.1142/9789812563071_0035.

14. Altepeter J B, Jefrey E R, Kwiat P G, Photonic state tomography, Adv At Mol Phys, 52(2005)105-159.

15. Werner R F. Quantum states with Einstein-Podolsky-Rosen correlations admitting a hidden-variable model, Phys Rev A, 40(1989)4277-4281.

16. White A G, James D F V, Munro W F V, Kwiat P G, Exploring Hilbert space: Accurate characterization of quantum information, Phys Rev A, 65(2001)012301; doi.org/10.1103/PhysRevA.65.012301.

17. Puentes G, Aiello A, Voight D, Woerdman J P, Entangled mixed-state generation by twin-photon scattering, Phys Rev A, 75(2007)032319; doi.org/10.1103/PhysRevA.75.032319.

18. Ghosh N, Vitkin I A, Tissue polarimetry: concepts, challenges, applications and outlook, J Biomed Opt, 16(2011) 110801; doi.org/10.1117/1.3652896.

Vol. 29 Nos 5-7, 2020, 387-394

Supercontinuum light source

Lingyan Shi

²Department of Bioengineering, University of California San Diego, La Jolla, CA-92093, USA

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

The unique spectral and temporal qualities of supercontinuum light sources are advancing our understanding of reactions in biology, chemistry and condensed matter. The panoply of applications of supercontinuum was reviewed here. © Anita Publications. All rights reserved.

Keywords: Supercontinuum, Absorption windows, Fiber laser, Golden Window, Mid-IR

References

1. (a) Alfano R R, Shapiro S L, Emission in the region 4000–7000 A via four-photon coupling in glass, Phys Rev Lett, 24(1970)584-587. (b) Alfano R R, Shapiro S L, Observation of self-phase modulation and small scale filaments in crystals and glasses, Phys Rev Lett, 24 (1970)592-594. (c) Alfano R R, Shapiro S L, Direct distortion of electronic clouds of rare-gas atoms in intense electric fields, Phys Rev Lett, 24 (1970)1219-1222.

2. Ranka J K, Windeler R S, Stentz A J, Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm, Opt Lett, 25(2000)25-27.

3. Dudley J M, Taylor J R, (eds) Supercontinuum Generation in Optical Fibers. (Cambridge University Press, Cambridge, England), 2010.

4. Alfano R R, Shi L, Supercontinuum microscope for resonance and non-resonance enhanced linear and nonlinear time resolved microscope for tissue and materials. U.S. Patent Appln No. 15409303, 2017.

5. Alfano R R, Shapiro S L, Picosecond spectroscopy using the inverse Raman effect, Chem Phys Lett, 8(1971)631-633.

6. Alfano R R, (ed), The Supercontinuum Laser Source: The Ultimate White Light, (Springer, New York), 2016.

7. Alfano R R. US Patents #9,414,887 B2, Aug. 16 2016 and # 9,561,077 B2, Feb. 7, 2017.

8. Nishizawa N, Chen Y, Hsiung P, Ippen E P, Fujimoto J G, Real-time, ultrahigh-resolution, optical coherence tomography with an all-fiber, femtosecond fiber laser continuum at 1.5 µm, Opt Lett, 29(2014)2846-2848.

9. Shi L, Alfano R R, Deep imaging in tissue and biomedical materials, (Pan Stanford Publishing, Singapore), 2017.

10. Shi L, Sordillo L A, Rodriguez-Contreras A, Alfano R R, Transmission in near- infrared optical windows for deep brain imaging, J Biophotonics, 9(2016)38-43.

11. Sriramoju V, Alfano R R, In vivo studies of ultrafast near-infrared laser tissue bonding and wound healing, J Biomed Opt, 20(2015)108001; doi.org/10.1117/1.JBO.20.10.108001.

12. Shi L, Sharanov M, Budansky Y, Rodríguez-Contreras A, Alfano R R, Deep Brain Imaging using the Near-Infrared Golden Optical Window Wavelengths, Biomedical Optics 2016, OSA Technical Digest (Optical Society of America, 2016), paper JW3A.43.

13. Mazhar SFB, Meyer H J, Samuels T, Sharonov M, Shi L, Alfano R R, Explanation of the competition between O-and E-wave induced stimulated Raman and supercontinuum in calcite under ultrafast laser excitation, Appl Opt, 59(2020)5252-5257.

14. Sordillo L A, Shi L, Sordillo D C, Sordillo P P, Alfano R R, Advances in medical applications using SWIR light in the wavelength range from 1000 to 2500 nm, Proc SPIE 10873, Optical Biopsy XVII: Toward Real-Time Spectroscopic Imaging and Diagnosis, (2019) 108730T.

15. Sordillo L A, Sordillo D C, Shi L, Sordillo P P, Alfano R R, SWIR windows as an adjunctive to biopsy for distinguishing and monitoring benign and malignant tissues, Proc SPIE 11234, Optical Biopsy XVIII: Toward Real-Time Spectroscopic Imaging and Diagnosis, (2020)112341H.

16. Shi L, Alfano R R, Future supercontinuum microscope for medical and biological applications, Conference on Lasers and Electro-Optics, OSA Technical Digest (Optical Society of America, 2017), paper AF2A.4.

17. Alfano R R, Sordillo L, Pu Y, Shi L, Deep optical imaging of tissue with less scattering in the second, third and fourth NIR spectral windows using supercontinuum and other laser coherent light sources, US Patent #10123705, Nov 13, 2018.

Vol. 29 Nos 5-7, 2020, 395-404

Detection and evaluation of solid tumors using fluorescence spectroscopy

Laura A Sordillo^1,2 and Peter P Sordillo^1,3

¹Institute for Ultrafast Spectroscopy and Lasers, Department of Physics at The City College of the City University of New York,

160 Convent Avenue, New York, NY 10031, USA

²The Grove School of Engineering, Department of Electrical Engineering at The City College of the City University of New York,

160 Convent Avenue, New York, NY 10031, USA

³Lenox Hill Hospital, Northwell Network, Department of Medicine, 100 East 77th Street, New York, NY 10075, USA

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

Robert R Alfano, director and founder of the Institute for Ultrafast Spectroscopy and Lasers (IUSL) at the City College of New York, pioneered the field of optical biopsy, when, in the 1980’s, he and his colleagues used fluorescence spectroscopy to distinguish normal from malignant tissues. That study, as well as many other studies by Alfano et al, initiated the field of optical biopsy, which applies light’s unique properties to assess disease. Nowadays, fluorescence spectroscopy is widely used in the evaluation of disease. Fluorescent spectral profiles from breast cancer tissues based on relative tryptophan (a key biomarker) content have been utilized in the investigation of the degree of malignancy in patients with high grade breast carcinoma. Label-free fluorescence spectroscopy has also been used in the study of tryptophan and tryptophan metabolites in neurodegenerative diseases like Alzheimer’s and Parkinson’s. This optical technique is a non-invasive, rapid, real time assessment of disease. It may be utilized as part of the evaluation for determining whether a cancer has been completely resected, thus reducing the requirement for second or repeat surgeries. Optical devices based on the emission properties of key biomarkers in tissue can be engineered to be compact and efficient and can provide an objective measure for assessing disease as well as different degrees of aggressiveness among the sub-group of tumors. Optical biopsy offers a noninvasive, or minimally invasive, tool for assessment of diseases, using light. © Anita Publications. All rights reserved.

Keywords: Fluorescence spectroscopy, Stokes shift spectroscopy, Tryptophan, NADH, Optical biopsy, Breast cancer, Solid tumors

References

1. Alfano R R, Tata T D, Cordero D B, Tomashefsky P, Longo F, Alfano M, Laser induced fluorescence spectroscopy from native cancerous and normal tissue, IEEE J Quantum Electron, 20(1984)1507-1511.

2. Alfano R R, Tang G, Pradhan A, Lam W, Choy D, Opher E, Fluorescence spectra from cancerous and normal human breast and lung tissues, IEEE J Quantum Electron, 23(1987)1806-1811.

3. Das B B, Liu F, Alfano R R, Time-resolved fluorescence and photon migration studies in biomedical and model random media, Rep Prog Phys, 60(1997)227; doi.org/10.1088/0034-4885/60/2/002.

4. Yoo K M, Alfano R R, Time-resolved coherent and incoherent components of forward light scattering in random media, Opt Lett, 15(1990)320-322.

5. Pu Y, Wang W B, Das B B, Achilefu S, Alfano R R, Time-resolved fluorescence polarization dynamics and optical imaging of Cytate: a prostate cancer receptor-targeted contrast agent, Appl Opt, 47(2008)2281-2289.

6. Sordillo L A, Das B B, Pu Y, Liang K, Milione G, Sordillo P P, Achilefu S, Alfano R R, Time-resolved fluorescence for breast cancer detection using an octreotate-indocyanine green derivative dye conjugate, Proc SPIE, Optical Biopsy XI, 8577(2013)857708; doi.org/10.1117/12.2003102.

7. Pu Y, Wang W B, Tang G C, Zeng F, Achilefu S, Vitenson J H, Sawczuk I, Peters S, Lombardo J M, Alfano R R, Spectral polarization imaging of human prostate cancer tissue using a near-infrared receptor-targeted contrast agent, Technol Cancer Res T, 4(2005)429-436.

8. Sordillo L A, Pu Y, Pratavieira S, Budansky Y, Alfano R R, Deep optical imaging of tissue using the second and third near-infrared spectral windows, J Biomed Opt, 19(2014)056004; doi.org/10.1117/1.JBO.19.5.056004.

9. Sordillo D C, Sordillo L A, Sordillo P P, Shi L, Alfano R R, Short wavelength infrared optical windows for evaluation of benign and malignant tissues, J Biomed Opt, 22(2017)045002; doi.org/10.1117/1.JBO.22.4.045002.

10. Sordillo L A, Lindwasser L, Budansky Y, Leproux P, Alfano R R, Imaging of tissue using a NIR supercontinuum laser light source with wavelengths in the second and third NIR optical windows, Proc SPIE, Optical Tomography and Spectroscopy of Tissue XI, 9319(2015), 93191Y; doi.org/10.1117/12.2078435.

11. Sordillo L A, Pratavieira S, Pu Y, Salas-Ramirez K, Shi L, Zhang L, Budansky Y, Alfano R R, Third therapeutic spectral window for deep tissue imaging, Proc SPIE, Optical Biopsy XII, 8940(2014)89400V; doi.org/10.1117/12.2040604.

12. Sordillo L A, Pu Y, Sordillo P P, Budansky Y, Alfano R R, Second and third NIR optical windows for imaging of bone microfractures, Proc SPIE, Biophotonics: Photonic Solutions for Better Health Care IV, 9129(2014)912912; doi.org/10.1117/12.2051917.

13. Sordillo L A, Pu Y, Sordillo P P, Budansky Y, Alfano R R, Deep tissue imaging of microfracture and non-displaced fracture of bone using the second and third near-infrared therapeutic windows, Proc SPIE, Photonic Therapeutics and Diagnostics X, 8926(2014)89263V; doi.org/10.1117/12.2046706.

14. Sordillo L A, Shi L, Sordillo D C, Sordillo P P, Alfano R R, Advances in medical applications using SWIR light in the wavelength range from 1000 to 2500 nm, Proc SPIE, Optical Biopsy XVII: Toward Real-Time Spectroscopic Imaging and Diagnosis, 10873(2019)108730T; doi.org/10.1117/12.2513382.

15. Sordillo D C, Sordillo L A, Sordillo P P, Alfano R R, Optical spectroscopy methods to probe key spectral fingerprints of animal bone, Proc SPIE, Photonic Therapeutics and Diagnostics IX, 8565(2013)856568; doi.org/10.1117/12.2005647.

16. Sordillo L A, Sordillo P P, Alfano R R, Imaging using a supercontinuum laser to assess tumors in patients with breast carcinoma, Proc SPIE, Optical Biopsy XIV: Toward Real-Time Spectroscopic Imaging and Diagnosis, 9703(2106)97031Z; doi.org/10.1117/12.2240512.

17. Sordillo D C, Sordillo L A, Shi L, Budansky Y, Sordillo P P, Alfano R R, Novel, near-infrared spectroscopic, label-free, techniques to assess bone abnormalities such as Paget’s disease, osteoporosis and bone fractures, Proc SPIE, Photonic Therapeutics and Diagnostics XI, 9303(2015)93033Z; doi.org/10.1117/12.2181314.

18. Sordillo L A, Lukas L, Yury B, Leproux P, Alfano R R, Near-infrared supercontinuum laser beam source in the second and third near-infrared optical windows used to image more deeply through thick tissue as compared with images from a lamp source, J Biomed Opt, 20(2015)1; doi.org/10.1117/1.JBO.20.3.030501.

19. Sordillo L A, Shi L, Bhagroo S, Nguyen T, Lubicz S, Pu Y, Budansky Y, Hatak N Alfano R R, Spatial frequencies from human periosteum at different depths using two-photon microscopic images, Proc SPIE, Photonic Therapeutics and Diagnostics X, 8926(2014)892642; doi.org/10.1117/12.2045476.

20. Liu CH, Boydston-White S, Weisberg A, Wang W, Sordillo L A, Perotte A, Tomaselli V P, Sordillo P P, Pei Z, Shi L, Alfano, RR,Vulnerable atherosclerotic plaque detection by resonance Raman spectroscopy, J Biomed Opt, 21(2016)127006; doi.org/10.1117/1.JBO.21.12.127006.

21. Liu C H, Boydston-White S, Wang W, Sordillo L A, Shi L, Weisberg A, Tomaselli V P, Sordillo P P, Alfano R R, Optical pathology study of human abdominal aorta tissues using confocal micro resonance Raman spectroscopy, Proc SPIE, Optical Biopsy XIV: Toward Real-Time Spectroscopic Imaging and Diagnosis, 9703(2016)97031S; doi.org/10.1117/12.2213368

22. Liu C H, Wu B, Sordillo L, Boydston-White S, Sriramoju V, Zhang C, Beckman H, Zhang L, Pei Z, Shi L, Alfano R R, Assessment of basal cell carcinoma from normal human skin tissues using Resonance Raman spectroscopy, Proc OSA, Frontiers in Optics, (2018) JTu3A-118; doi.org/10.1364/FIO.2018.JTu3A.118

23. Sordillo L A, Zhang L, Shi L, Sriramoju V, Sordillo P P, Alfano R R, Resonance Raman and fluorescence spectroscopy to evaluate increased brain kynurenine pathway activity in samples from patients with neurodegenerative disease, Proc SPIE, Biomedical Imaging and Sensing Conference, 10711(2018)107111F; doi.org/10.1117/12.2317118.

24. Liu C H, Sriramoju V, Boydston-White S, Wu B, Zhang C, Pei Z, Sordillo L A, Beckman H, Alfano R R, Resonance Raman of BCC and normal skin, Proc SPIE, Optical Biopsy XV: Toward Real-Time Spectroscopic Imaging and Diagnosis, 10060(2017)100601B; doi: 10.1117/12.2254628

25. Liu C H, Wu B, Boydston-White S, Beckman H, Sriramoju V, Sordillo L, Zhang C, Smith J, Zhang L, Shi L, Alfano R R, Characterization and discrimination of basal cell carcinoma and normal human skin tissues using resonance Raman spectroscopy, Proc OSA, Frontiers in Optics (2017), paper JTu2A-72; doi.org/10.1364/FIO.2017.JTu2A.72.

26. Liu C H, Das B B, Glassman W S, Tang G C, Yoo K M, Zhu H R, Akins D L, Lubicz S S, Cleary J, Prudente R, Celmer E, Raman, fluorescence, and time-resolved light scattering as optical diagnostic techniques to separate diseased and normal biomedical media, J Photoch Photobio B, 16(1992)187-209.

27. Pu Y, Wang W, Yang Y, Alfano R R, Stokes shift spectroscopy highlights differences of cancerous and normal human tissues, Opt Lett, 37(2012)3360-3362.

28. Pu Y, Wang W, Yang Y, Alfano RR, Stokes shift spectroscopic analysis of multifluorophores for human cancer detection in breast and prostate tissues, J Biomed Opt, 18(2013)017005; doi.org/10.1117/1.JBO.18.1.017005

29. Pu Y, Wang W, Tang G C, Alfano R R, Changes of collagen and nicotinamide adenine dinucleotide in human cancerous and normal prostate tissues studied using native fluorescence spectroscopy with selective excitation wavelength, J Biomed Opt, 15(2010)047008; doi.org/10.1117/1.3463479.

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34. Sordillo L A, Zhang L, Sordillo P P, Alfano R R, Alzheimer’s disease: label-free fluorescence shows increases in indoleamine 2, 3-dioxygenase (IDO) or tryptophan 2, 3-dioxygenase (TDO) activity in affected areas of the brain. Proc SPIE, Optical Biopsy XVII: Toward Real-Time Spectroscopic Imaging and Diagnosis, 10873(2019)108731C; doi.org/10.1117/12.2513384.

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Vol. 29 Nos 5-7, 2020, 405-414

Stokes’shift spectroscopy for quality control in the manufacture of quantum dot nano crystals

V Masilamai^1,2,3, M J Aljaafreh² , M S AlSalhi^1,2, G I Al-Faggy², M M Albeyali² and Sradh Prasad^1,2

¹Research Chair on laser diagnosis of cancers, Department of Physics and Astronomy,

College of Science, King Saud University, Riyadh 11451, Saudi Arabia

²Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451, Saudi Arabia

³Masila’s Research Center, Thiruppangili- 621 005, India

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

Quantum dots (QDs) are a new class of nano-materials with wide range of applications in optoelectronics, biosensors sensitized cancer detection and therapy. About fifty such quantum dots, CdS, CdSe, CdTe and ZnCuInS etc are available in the market. They are produced mostly by wet chemistry with careful control of temperature and pressure as well as composition of component materials. Another technique is the plasma synthesis, though the former one is overwhelmingly predominant because of better control of the size of the particular quantum dots. The photo- and electroluminescence properties of these QDs are strongly dependent on the composition of the elements and also their size, the latter one being usually determined by the transmission electron microscope (TEM). The present report is on an inexpensive easy-to-do innovative technique for maintaining the quality control (such as purity and size) of the manufacture of any type of QDs (such as CdTe) and nano-material (nano-gold). This technique is based on synchronous luminescence spectroscopy (SLS) and an impurity as low as 3 % of QD of same material or another could be detected. The instrumentation is so simple and compact that it can be coupled to any manufacturing unit so that quality control could be accomplished online. © Anita Publications. All rights reserved.

Keywords: Quantum dots, Photoluminescence emission spectrum, Electroluminescence properties, Synchronous luminescence spectroscopy, Transmission electron microscope.

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Vol. 29 Nos 5-7, 2020, 415-421

Light–matter interaction in 2D semiconductors

Vinod M Menon ^1,2

¹Department of Physics, City College of New York, 160 Convent Ave., New York, NY 10031

² Graduate Center of the City University of New York, 365 Fifth Ave., New York, NY 10016

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

In this short review article, we discuss the role of 2D semiconductors based on transitional metal dichalcogenides for photonics. We discuss the unique properties that make them interesting both from a fundamental and technological standpoint. Specifically, we present recent work in the area of optical control of the valley degree of freedom and strong light-matter coupling in these materials. We finally discuss future directions and potential applications. © Anita Publications. All rights reserved.

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Vol. 29 Nos 5-7, 2020, 423-431

High-resolution spectra of self-phase modulation in optical fibers

Q Z Wang¹ and P P Ho²

¹Technology Center 2600, United States Patent and Trademark Office, 501 Dulany Street, Alexandria, VA 22314

²Institute of Ultrafast Spectroscopy and Lasers, Department of Electrical Engineering,

The City College of The City University of New York, 138th Street and Convent Avenue, New York, New York 10031

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

This paper is dedicated to Prof Alfano for his insight, inspiration and tutelage in the work present here. We review here theoretical calculations and experimental measurements of self-phase-modulation spectra generated with picosecond laser pulses at 532 and 1064 nm propagating in optical fibers. The spectral structures of self-phase-modulation spectra are observed with a high-resolution optical spectral analysis system. The experimental observations are in good agreement with the theoretical predictions. Alfano. © Anita Publications. All rights reserved.

Keywords: SPM, Optical fibers, Supercontinuum, Nonlinear index of refraction, n₂.

References

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18. Pu Y, Wang W B, Yang Y, Alfano R R, Stokes shift spectroscopy highlights differences of cancerous and normal human tissues, Opt Lett, 37(2012)3360-3362.

19. Sordillo L A, Pu Y, Prativieira S, Budansky Y, Alfano R R, Deep optical imaging of tissue using the second and third near-infrared spectral windows, J Bio Opt, 19(2014)056004; doi.10.1117/1.JBO.19.5.056004.

20. Rumala Y R, Dorsinville R, Alfano R R, Current applications of supercontinuum light, in The Supercontinuum Laser Source, Chapter 11, (ed) Alfano R R, (Springer-Verlag, NewYork), 2016.

21. Smirnov S V, Ania-Castanon J D, Kobtsev S, Turitsyn S K, Supprcontinuumn in telecom applications, in The Supercontinuum Laser Source, Chapter 10, (ed) Alfano R R, (Springer-Verlag, NewYork), 2016.

22. Heidt A, Hartung A, Bartel B, Generation of Ultrafast and Coherent Supercontinuum Light Pulses in All –Normal Dispersion Fibers, in The Supercontinuum Laser Source, Chapter 6, (ed) Alfano R R, (Springer-Verlag, NewYork), 2016.

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Vol. 29 Nos 5-7, 2020, 433-446

Nonlinear optical processes in medical diagnostics and imaging

B B Das

Fairfield University, Fairfield, Connecticut, USA

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

This is a short review of various nonlinear processes of harmonic generation and multi-photon excitation for possible applications in medical diagnostics and imaging. Various parameters that influence spatial resolution and penetration depth in single-photon to four-photon excitation processes are analyzed. Second harmonic signal for subsurface cancer imaging, steady-state two-photon excitation imaging of tryptophan distribution, in vivo multi-photon microscopy for deep brain imaging, and picosecond time-resolved multi-photon fluorescence for early detection of Alzheimer’s disease are explored. © Anita Publications. All rights reserved.

Keywords: Multi-photon excitation, Two-photon absorption, Three-photon, Four photon, Second harmonic generation imaging, Time-resolved fluorescence, Multi-photon microscopy.

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25. Chan F T S, Schierle G S K, Kumita J R, Bertoncini C W, Dobson C M, Kaminski C F, Protein amyloids develop an intrinsic fluorescence signature during aggregation, Analyst, 138(2013)2156-2162.

26. Das B B, Shi L, Budansky Y, Rodríguez-Contreras A, Alfano R R, Alzheimer mouse brain tissue measured by time-resolved fluorescence spectroscopy using single- and multi-photon excitation of label free native molecules, J Biophotonics, 11(2018)1-8.

27. Hardy J, Selkoe D J, The Amyloid Hypothesis of Alzheimer’s Disease: Progress and Problems on the Road to Therapeutics, Science, 297(2002)353-356.

28. Ossenkoppele R, Janse W J, Rabinovici G D, D. Knol D L, van der Flier W M, van Berckel B N M, Scheltens P, Visser P J, Prevalence of Amyloid PET Positivity in Dementia Syndromes A Meta-analysis, JAMA, 313(2015)1939-1949.

29. Jansen W J, Ossenkoppele R, Knol D L, Tijms B M, Scheltens P, Verhey F R J, Visser P J, Prevalence of Cerebral Amyloid Pathology in Persons Without Dementia A Meta-analysis, JAMA, 313(2015)1924-1938.

30. Shi L, Lu L, Harvey G, Harvey T, Rodríguez-Contreras A, Alfano R R, Label-Free Fluorescence Spectroscopy for Detecting Key Biomolecules in Brain Tissue from a Mouse Model of Alzheimer’s Disease, Nature Scientific Reports, 7(1917)2599; doi:10.1038/s41598-017-02673-5.

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Vol. 29 Nos 5-7, 2020, 447-460

Intense, femtosecond laser excited solid plasmas

A D Lad, M Shaikh, K Jana, Y M Ved and G R Kumar

Tata Institute of Fundamental Research,

1 Homi Bhabha Road, Colaba, Mumbai- 400 005, India

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

High energy density science got a major boost with the invention of compact, table-top, high peak power femtosecond lasers. High intensity (>10¹⁸ W/cm²), ultrashort (~25 fs) pulses produce near- solid density, high temperature plasma on a solid target surface and launch mega-ampere electron pulses into the solid. Higher picosecond laser intensity contrast (~10⁹) results in efficient coupling of peak laser energy to the plasma electrons thereby enhancing the density and temperature. In this paper, we present a survey of some of the recent work done in this area at the Tata Institute of Fundamental Research, Mumbai, India. We also demonstrate a variety of diagnostics (some of which we have advanced) to study the generation and propagation of these hot electron pulses and consequences of such transport deep in the target. We present high resolution measurements of the critical surface of hot, dense laser-produced plasma employing two-colour, pump-probe reflectivity and Doppler spectrometry. These measurements help us understand the rapid motion of the critical density layer in the plasma as well as the generation and propagation of shock waves. Spatio-temporal evolution of self-generated mega-gauss magnetic fields is presented. The time evolution of the magnetic pulse provides crucial information on the conductivity of hot, dense matter, not easily measurable otherwise. We compare results with those obtained using low-contrast, intense laser pulses. © Anita Publications. All rights reserved.

Keywords: High intensity lasers, Ultrashort pulses, Femtosecond pulses, Laser produced plasmas, Giant magnetic fields, Plasma instabilities, Doppler spectrometry, Relativistic electron transport

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11. Baton S D, Santos J J, Amiranoff F, Popescu H, Gremillet L, Koenig M, Martinolli E, Guilbaud O, Rousseaux C, Rabec Le Gloahec M, Hall T, Batani D, Perelli E, Scianitti F, Cowan T E, Evidence of Ultrashort Electron Bunches in Laser-Plasma Interactions at Relativistic Intensities, Phys Rev Lett, 91(2003)105001; doi.org/10.1103/PhysRevLett.91.10500.

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13. Shaikh M, Lad A D, Birindelli G, Pepitone K, Jha J, Sarkar D, Tata S, Chatterjee G, Dey I, Jana K, Singh P K, Tikhonchuk V T, Rajeev P P, Kumar G R, Mapping the Damping Dynamics of Mega-Ampere Electron Pulses Inside a Solid, Phys Rev Lett, 120(2018)065001; doi.org/10.1103/PhysRevLett.120.065001.

14. Shaikh M, Lad A D, Sarkar D, Jana K, Kumar G R, Rajeev P P, Measuring the lifetime of intense-laser generated relativistic electrons in solids via gating their Cherenkov emission, Rev Sci Instrum, 90(2019)013301; doi.org/10.1063/1.5054785.

15. Singh P K, Chatterjee G, Lad A D, Adak A, Ahmed S N, Sood A K, Khorasaninejad M, Adachi M M, Karim K S, Saini S S, Kumar G R, Efficient generation and guiding of megaampere relativistic electron current by silicon nanowires, App Phys Lett, 100(2012)244104; doi.org/10.1063/1.4729010.

16. Chatterjee G, Singh P K, Ahmed S N, Robinson A P L, Lad A D, Mondal S, Narayanan V, Srivastava I, Koratkar N, Pasley J, Sood A K, Kumar G R, Macroscopic Transport of Mega-ampere Electron Currents in Aligned Carbon-Nanotube Arrays, Phys Rev Lett, 108(2012)235005; doi.org/10.1103/PhysRevLett.108.235005.

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18. Singh P K, Cui Y Q, Adak A, Lad A D, Chatterjee G, Brijesh P, Sheng Z M, Kumar G R, Contrasting levels of absorption of intense femtosecond laser pulses by solids, Sci Rep, 5(2015)17870; doi.org/10.1038/srep17870.

19. (a) Habara H, Ohta K, Tanaka K A, Kumar G R, Krishnamurthy M, Kahaly S, Mondal S, Bhuyan M K, Rajeev R, Zheng J, Direct, Absolute, and In Situ Measurement of Fast Electron Transport via Cherenkov Emission, Phys Rev Lett, 104(2010)055001; doi.org/10.1103/PhysRevLett.104.055001. (b) Habara H, Ohta K, Tanaka K A, Kumar G R, Krishnamurthy M, Kahaly S, Mondal S, Bhuyan M K, Rajeev R, Zheng J, Measurements of high energy density electrons via observation of Cherenkov radiation, Phys Plasmas, 17(2010)056306; doi.org/10.1063/1.3346370.

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21. Sandhu A S, Dharmadhikari A K, Rajeev P P, Kumar G R, Sengupta S, Das A, Kaw P K, Laser-Generated Ultrashort Multimegagauss Magnetic Pulses in Plasmas, Phys Rev Lett, 89(2002)225002; doi.org/10.1103/PhysRevLett.89.225002.

22. Kahaly S, Mondal S, Kumar G R, Sengupta S, Das A, Kaw P K, Polarimetric detection of laser induced ultrashort magnetic pulses in overdense plasma, Phys Plasmas, 16(2009)043114; doi.org/10.1063/1.3118586.

23. Mondal S, Narayanan V, Ding W J, Lad A D, Hao B, Ahmed S N, Wang W M, Sheng Z M, Sengupta S, Kaw P K, Das A, Kumar G R, Direct observation of turbulent magnetic fields in hot, dense laser produced plasmas, Proc Natl Acad Sci USA, 109(2011)8011; doi.org/10.1073/pnas.1200753109.

24. Chatterjee G, Singh P K, Adak A, Lad A D, Kumar G R, High-resolution measurements of the spatial and temporal evolution of megagauss magnetic fields created in intense short-pulse laser-plasma interactions, Rev Sci Instrum, 85(2014)013505; doi.org/10.1063/1.4861535.

25. Shaikh M, Lad A D, Jana K, Sarkar D, Dey I, Kumar G R, Megagauss magnetic fields in ultra-intense laser generated dense plasmas, Plasma Phys Control Fusion, 59(2016)014007; doi.org/10.1088/0741-3335/59/1/014007.

26. Kahaly S, Yadav S K, Wang W M, Sengupta S, Sheng Z M, Das A, Kaw P K, Kumar G R, Near-Complete Absorption of Intense, Ultrashort Laser Light by Sub-λ Gratings, Phys Rev Lett, 101(2208)145001; doi.org/10.1103/PhysRevLett.101.145001.

27. Rajeev P P, Taneja P, Ayyub P, Sandhu A S, Kumar G R, Metal Nanoplasmas as Bright Sources of Hard X-Ray Pulses,Phys Rev Lett, 90(2003)115002; doi.org/10.1103/PhysRevLett.90.115002.

28. Cristoforetti G, Londrillo P, Singh P K, Baffigi F, D’Arrigo G, Lad A D, Milazzo R G, Adak A, Shaikh M, Sarkar D, Chatterjee G, Jha J, Krishnamurthy M, Kumar G R,Gizzi L A, Transition from Coherent to Stochastic electron heating in ultrashort relativistic laser interaction with structured targets, Sci Rep, 7(2017)1479; doi.org/10.1038/s41598-017-01677-5.

29. Sarkar D, Singh P K, Cristoforetti G, Adak A, Chatterjee G, Shaikh M, Lad A D, Londrillo P, D’Arrigo G, Jha J, Krishnamurthy M, Gizzi L A, Kumar G R, Silicon nanowire based high brightness, pulsed relativistic electron source, APL Photon, 2(2017)066105; doi.org/10.1063/1.4984906.

30. Mondal S, Chakraborty I, Ahmed S N, Carvalho D, Singh P S, Lad A D, Narayanan V, Ayyub P, Kumar G R, Zheng J, Sheng Z M, Highly enhanced hard x- ray emission from oriented metal nanorod arrays excited by intense femtosecond laser pulses, Phys Rev B, 83(2011)035408; doi.org/10.1103/PhysRevB.83.035408.

31. Singh P K, Chakraborty I, Chatterjee G, Adak A, Lad A D, Brijesh P, Ayyub P, Kumar G R, Enhanced transport of relativistic electrons through nanochannels, Phys Rev Spec Topics-Accel Beams, 16(2013)063401; doi.org/10.1103/PhysRevSTAB.16.063401.

32. Bagchi S, Kiran P P, Yang K, Rao A M, Bhuyan M K, Krishnamurthy M, Kumar G R, Bright, low debris, ultrashort hard x-ray table top source using carbon nanotubes, Phys Plasmas, 18(2011)014502; doi.org/10.1063/1.3531685.

33. Krishnamurthy M, Mondal S, Lad A D, Bane K, Ahmed S N, Narayanan V, Rajeev R, Chatterjee G, Singh P K, Kumar G R, Kundu M, Ray K, A bright point source of ultrashort hard x-ray pulses using biological cells, Opt Exp, 20(2012)5754; doi.org/10.1364/OE.20.005754.

34. Krishnamurthy M Kundu M, Bane K, Lad A D, Singh P K, Chatterjee G, Kumar G R, Ray K, Enhanced x-ray emission from nano-particle doped bacteria, Opt Exp, 23(2015)17909; doi.org/10.1364/OE. 23.017909.

35. Sandhu A S, Kumar G R, Sengupta S, Das A, Kaw P K, Laser-Pulse-Induced Second-Harmonic and Hard X-Ray Emission: Role of Plasma-Wave Breaking, Phys Rev Lett, 95(2005)025005; doi.org/10.1103/PhysRevLett.95.025005.

36. Adak A, Robinson A P L, Singh P K, Chatterjee G, Lad A D, Pasley J Kumar G R, Terahertz Acoustics in Hot Dense Laser Plasmas, Phys Rev Lett, 114(2015)115001; doi.org/10.1103/PhysRevLett.114.115001.

37. Teubner U, Gibbon P, High-order harmonics from laser-irradiated plasma surfaces, Rev Mod Phys, 81(2009)445; doi.org/10.1103/RevModPhys.81.445.

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39. Singh P K, Adak A, Lad A D, Chatterjee G, Brijesh P, Kumar G R, Controlling two plasmon decay instability in intense femtosecond laser driven plasmas, Phys Plasmas, 22(2015)113114; doi.org/10.1063/1.4935909.

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43. Snavely R A, Zhang B, Akli K, Chen Z, Freeman R R, Gu P, Hatchett S P, Hey D, Hill J, Key M H, Izawa Y, King J, Kitagawa Y, Kodama R, Langdon A B, Lasinski B F, Lei A, MacKinnon A J, Patel P, Stephens R, Tampo M, Tanaka K A, Town R, Toyama Y, Tsutsumi T, Wilks S C, Yabuuchi T, Zheng J, Laser generated proton beam focusing and high temperature isochoric heating of solid matter, Phys Plasmas, 14(2007)092703; doi.org/10.1063/1.2774001.

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Vol. 29 Nos 5-7, 2020, 463-472

Breaking symmetry to steer light through multi-channel photonic crystal waveguides

Gagandeep Kaur1 and Harshawardhan Wanare^1,2

¹Centre for Lasers and Photonics, Indian Institute of Technology Kanpur, Kanpur, India

²Department of Physics, Indian Institute of Technology Kanpur, Kanpur, India

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

We present a new control paradigm that uses a weak perturbation to control light flow across multiple channels in a photonic crystal cavity-waveguide structure. Introduction of a weak perturbation simultaneously breaks the symmetry of the underlying structure and leads to creation of robust spatial mode superpositions that transform the cavity-waveguide coupling. In particular, we demonstrate this control for a variety of spatial modes including dipole, quadrupole and hexapole modes in a hexagonal photonic crystal lattice. The eigen energies of the modes, their spatial alignment and their superpositions can all be engineered precisely through the weak perturbation. We also study the effect of introducing strong perturbation on the cavity modes, wherein the interplay between the global and the local symmetry plays a central role. We present numerical simulations involving the finite difference time domain technique that demonstrate effective control over transmission across multi-port waveguide channels. © Anita Publications. All rights reserved.

Keywords: Photonic crystals, Point and linear defects.

Total Refs : 11

Vol. 29 Nos 5-7, 2020, 473-481

Polarization controlled highly regular laser induced periodic surface structures: a look at its origin and its application towards perfect absorption of light

Mudasir H Dar¹, L Jyothi² and D Narayana Rao^2*

¹Department of Physics, Govt Degree College, Anantnag, Khannabal-192 101, (J&K), India

²School of Physics, University of Hyderabad, Prof C R Rao Road, Gachibowli, Hyderabad- 500 046, India

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

Controlling the surface morphology at nanometer scale is an important feature in modern nanophotonics. In this article, we report the fabrication of Laser Induced Periodic Surface Structures (LIPSS) on different metals, using a simple and single step experimental technique of Laser Direct Writing (LDW). Our aim is to look for candidates suitable for the formation of highly regular LIPSS and optimize the laser irradiation conditions to control the orientation and period of the LIPSS formation. We study the interaction of linearly polarized femtosecond laser beam at 800 nm wavelength with different metals towards the formation of LIPSS. We analyze our results on the basis of decay lengths of the excited Surface Plasmon Polaritons (SPPs) on the laser irradiated metal surface. Among the metals studied, highly regular LIPSS could be fabricated only on Mo, Ni, Fe and Ti. The metals with large SPP decay lengths do not appear to be the potential candidates for the fabrication of regular periodic structures. Our achievements may find potential importance in laser writing technology towards development of surface nanostructure related applications, specifically towards a perfect light absorbing surface. © Anita Publications. All rights reserved.

Keywords: Laser direct writing, Surface plasmon polaritons, Surface structures

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Vol. 29 Nos 5-7, 2020, 483-490

Measuring absolute phase in homodyne mode frequency domain fluorescence optical tomography

N C Biswal¹, A Maslowski², J Jagtap³, T Wareing², J McGhee², and A Joshi³

¹Department of Radiation Oncology,University of Maryland School of Medicine, Baltimore, MD 21201 1559, USA

²Transpire Inc., Gig Harbor, WA 98332 USA

³Departments of Biomedical Engineering and Radiology, Medical College of Wisconsin Milwaukee, WI 53226,USA

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

We report a method for measuring absolute phase lag maps on tissue boundary for frequency domain photon migration (FDPM) measurements made with image-intensified charge-coupled device cameras operating under the homodyne data acquisition mode. Current frequency domain fluorescence tomography schemes with homodyne data acquisition rely on various types of measurement data normalization/referencing methods for model-based image reconstruction because of the arbitrary unknown phase angle of the frequency domain near-infrared illumination source. We describe a setup that relies on imperfect fluorescence emission filters to capture the true excitation source phase measurements during emission data acquisition and show improvements in the conditioning of the radiative transport model–based image reconstruction.© Anita Publications. All rights reserved.

Keywords: Optical tomography, Frequency mode, Homodyne Mode, Absolute phase.

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Vol. 29 Nos 5-7, 2020, 493-500

Green synthesis of zinc oxide nanoparticles using Ocimum sanctum leaf extract for biomedical applications

Prashant Kharey¹, Surjendu Bikash Dutta², Amit³ and Sharad Gupta^1,3

¹Discipline of Metallurgy Engineering and Materials Science,
Indian Institute of Technology Indore, Khandwa Road, Indore -453 552, India

²Discipline of Physics, Indian Institute of Technology Indore, Khandwa Road, Indore- 453 552, India

³Discipline of Biosciences and Biomedical Engineering, Indian Institute of Technology Indore, Khandwa Road, Indore- 453 552, India

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

A green chemistry-based approach of nanoparticle synthesis is an eco-friendly, simple, and cost-effective way to fabricate nanoparticles .The primary aim of this study is to synthesise zinc oxide nanoparticles (ZnO NPs) with a simple green chemistry-based approach using plant leaf extract of an aromatic perennial plant, Ocimum sanctum, commonly known as Tulsi. The particles obtained by the green synthesis route are non-toxic and their surface is free from any chemical impurity. The structure, morphology, and optical absorption properties of these green synthesized ZnO NPs have been studied in detail. The XRD analysis depicts that nanoparticles are pure and crystalline. Electron microscopy images confirm that the particles are spherical, and the size distribution of these nanoparticles is estimated to be in the range of ~87±7nm. The MTT assay was accomplished on human cervical cancer (HeLa) cells and shows that the ZnO nanoparticles are biocompatible and thus safe for cells even at higher concentratons upto 600 μM. Results of this study suggest that that in the future, these green synthesized ZnO nanoparticles can be used for biomedical applications. © Anita Publications. All rights reserved.

Keywords: Nanotechnology, Pharmaceutics, Ocimum sanctum, Green chemistry, ZnO nanoparticles, Biocompatible.

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Vol. 29 Nos 5-7, 2020, 501-518

Native fluorescence spectroscopy of blood plasma of cervical cancer patients and normal subjects at 280 nm excitation: A feasibility study and preliminary report

K Muthuvelu¹, S Anandh², M Yuvaraj², G Einstein², P Aruna², and S Ganesan²

¹Barnard Institute of Radiology, Madras Medical College, Chennai- 600 006, India

²Department of Medical Physics, Anna University, Chennai- 600 025, India

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

Native fluorescence emission and excitation spectra of blood plasma protein were recoded and discriminated the normal subjects from different stages of cervical cancer patients using the native fluorescence emission spectra at 280 nm excitation and fluorescence excitation spectra for 340 nm emission maximum. A marked difference was observed in the spectral signatures between the blood plasma of normal subjects and the different stages of cervical cancer patients in both the fluorescence emission and excitation spectra. The possible reasons for the altered spectral signature may attributed to altered microenvironment of proteins which are present in the blood plasma during the transformation of normal into different conditions of cervical cancer. Based on the observed spectral difference an attempt has been made to determine the statistical significance. From the discriminant analysis for the fluorescence emission spectra at 280 nm excitation provides the 96.4 % specificity and 100% sensitivity and fluorescence excitation spectra for 340 nm emission provides 100 % specificity and 96.6 % sensitivity. Hence both the fluorescence emission and excitation spectra of blood plasma of normal and cervical cancer patients may be considered as an effective tool in diagnosing cervical cancer. © Anita Publications. All rights reserved.

Keywords: Cervical cancer, Native fluorescence spectroscopy, Blood plasma, Linear discriminant analysis.

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Vol. 29 Nos 5-7, 2020, 519-527

Synchronous fluorescence spectral intensity ratio mapping for early discrimination of epithelial cancers

Ebenezar Jeyasingh^{1, 2}, P Aruna¹, and S Ganesan¹

¹Department of Medical Physics, Anna University, Chennai – 600 025, India

²Present Address: PG & Research Department of Physics, Jamal Mohamed College (Autonomous), Tiruchirappalli-620 020, India

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

Synchronous fluorescence (SF) spectral intensity ratio mapping is used to detect early tissue transformation in 7,12-dimethylbenz (a) anthracene (DMBA) induced mouse skin carcinogenesis model. SF spectra were measured under in vivo conditions from 33 DMBA treated animals and 6 control animals in the wavelength region 250 – 600 nm at ∆λ = 20 nm. SF spectra show distinct bands and substantial variations between normal and different tissue transformation. During onset of neoplastic transformation, the epithelial tissues undergo biochemical, morphological and metabolic activity which in turn results in increased fluorescence intensity and spectral shift for tryptophan and NADH, and decreased fluorescence intensity for collagen, elastin, and FAD. Four statistically significant ratio parameters, namely I₃₅₀/I₃₇₅, I₃₅₀/I₃₈₆, I₃₅₀/I₄₀₀ and I₃₇₅/I₃₈₆ are identified, which showed same specificity and sensitivity based on the diagnostic scatter plots to discriminate normal from hyperplasia, hyperplasia from dysplasia, and dysplasia from WDSCC with specificities of 100%, 70%, and 100%, respectively and corresponding sensitivities of 100%, 70%, and 80%. © Anita Publications. All rights reserved.

Keywords: Synchronous Fluorescence, DMBA, Mouse skin, Carcinogenesis, Intensity Ratio, Epithelial cancers.

References

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Vol. 29 Nos 5-7, 2020, 529-537

Human tissue and saliva as diagnostic media for detection of oral cancer using stokes

shift spectroscopy: classification based on mahalanobis distance model

Pavan Kumar^{1, 2}, Kumar Ashutosh³ and Asima Pradhan^{2, 4}

¹Center for Biomedical Engineering (CBME), Indian Institute of Technology Ropar, Ropar-140 001, India

²Department of Physics, Indian Institute of Technology Kanpur, Kanpur-208 016, India

³Department of ENT, GSVM medical College, Kanpur-208 002, India

⁴Center for Laser and Photonics (CELP), IIT Kanpur, Kanpur-208 016, India

This article is dedicated to Prof Robert R Alfano for his tremendous contributions to the area of photonics

We have carried out a study between two diagnostic media, human oral tissue and saliva, for oral cancer detection by using Stokes shift (SS) spectroscopy (SSS) at offset (Δλ) of 120 nm. Measurements have been performed in three groups: oral squamous cell carcinoma (OSCC), dysplastic and control. An offset of 120 nm, captures changes from many of the contributing fluorophores present in both the media, discriminating well among the groups. SS spectra of tissue and saliva consist of major and minor bands of tryptophan, collagen, nicotinamide adenine dinucleotide (NADH), flavin adenine dinucleotide (FAD) and porphyrins. Principal component analysis (PCA) is employed on the data sets of SS spectra after which the classification among the groups is performed using Mahalanobis distance (MD) and receiver operating characteristic (ROC) analysis methods. For oral tissue, SS spectroscopy differentiates OSCC to normal, dysplasia to normal and OSCC to dysplasia with sensitivities 94 %, 89 %, 88 % and specificities 96 %, 80 %, 81 %, respectively. For saliva, respective groups are differentiated with sensitivities 94 %, 81 %, 91% and specificities 96 %, 96 %, 89 %. In differentiating OSCC to dysplasia in tissue and saliva, sensitivity and specificity values are found almost comparable but with higher overlap in the MD values. Since the results from human saliva and tissue samples are equally promising, therefore, human saliva may be used as a convenient substitute medium for oral cancer detection with 120 nm Stokes shift. © Anita Publications. All rights reserved.

Keywords: Oral cancer, Tissue & saliva, Stokes shift spectroscopy, Mahalanobis distance model, Principal component analysis, Receiver operating characteristic analysis

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