Author: G.V. Pavan Kumar

Namaste, Hola & Welcome from G.V. Pavan Kumar. I am a Professor of Physics at the Indian Institute of Science Education and Research, Pune, India. My research interests are : (1) Optics & Soft Matter: Optically Induced Forces – Assembly, Dynamics & Function; (2) History and Philosophy of Science – Ideas in Physical Sciences. I am interested in the historical and philosophical evolution of ideas and tools in the physical sciences and technology. I research the intellectual history of past scientists, innovators, and people driven by curiosity, and I write about them from an Indian and Asian perspective. My motivation is to humanize science. In the same spirit, I write and host my podcast Pratidhvani – Humanizing Science.

45. Scientific Gandhism

Thanks to Gautam Menon, I came across this article in Nature, which makes an interesting case for being self critical of one’s own published work.

Perhaps, this is a good way to go, although much easier said than done. Overall, I strongly support the line of thinking of looking inward and being critical of one’s work.

One of the motivations for writing my blog is to highlight the human element of doing science, and honest mistakes in the pursuit of science are very much part of it.

This is indeed a good culture to inculcate and encourage in a day and age where everything negative and critical is looked down upon as a disadvantage.

The article also reminds me of Peter Medawar’s talk: “Is the scientific paper a fraud?” , which was one of the most refreshing viewpoints on the pursuit of science that I have read. Interestingly, there has been quite a lot of debate on this question, and is worth exploring.

Also there is an element of Gandhism in being truthful to oneself and others, which is refreshing to see in scientific world :-)

44. Beaming light with a bent-nanowire

We have a new publication in Journal of Physical Chemistry Letters on the “Beaming Elastic and SERS Emission from Bent-Plasmonic Nanowire on a Mirror Cavity”

In short, we show, how by bending a nanowire we can narrowly beam the light scattered from molecules (see adjoining picture).

Optical emission from quantum objects such as atoms and molecules are very sensitive to their local surroundings. One of the current challenges in controlling optical emission from molecules at subwavelength scale is to narrow their scattering directivity. In the context of molecules, controlling light scattering at sub-wavelength scale has utility in optical trapping of molecules, molecular QED, cavity molecular mechanics, molecular quantum optics and many other areas of research. 

Thanks to the great effort by Sunny Tiwari in my lab, who in the middle of the pandemic, tirelessly executed the idea of beaming elastic and Raman scattering emission from molecules in the vicinity of a bent plasmonic silver nanowire resting on a metallic mirror.  He was ably supported by Adarsh (now at ETH), Dipta and Shailendra. Together, they experimentally confirmed the beaming characteristics from this geometry and corroborated with elaborate numerical simulations.

This work further motivates questions related to directivity control for single photon emitters and can be potentially harnessed for momentum-space engineering of nano-optical forces……

we say bend the light like a nanowire…Smile

DOI of JPCL article : https://doi.org/10.1021/acs.jpclett.1c01923

arxiv version :   https://arxiv.org/abs/2106.09347v1

43. Gadagkar’s article

Central to scientific thinking is the ability to create an idea, test it rigorously, and report the results. This thinking is made coherent and expressed in the form of writing. Scientific research indeed can be fostered and improved by writing well, especially when guided by the goals to achieve accuracy and clarity.

I recently read a wonderful article by Prof. Raghavendra Gadagkar, which elegantly makes a case for why scientist must write to a wider audience, and why the boundary between the roles of a scientist and a science writer should be diminished.

The article reads like a manifesto for science communication, as the author himself states at the end. I strongly recommend this article to anybody who is involved in pursuit of science.

Perhaps I will add one more point to what the author mentions. There might be a very important role for science writers who can take emerging developments in science literature and translate it into vernacular language. An authentic scientific voice in regional language can really impact not only the interest of students, but also of the general public, including policy makers and politicians.

India and the world needs more science, and scientific way of life. Therefore, doing science is as important as communicating it. Prof. Gadagkar’s article makes an excellent case for this.

42. New paper on WGMs via plasmonic nanowire

We have a new paper in Materials Research Bulletin to be published in a special issue on Recent Advances in Functional Materials

The paper is about “Sub-wavelength plasmon polaritons channeling of whispering gallery modes of fluorescent silica microresonator”

Individual spherical objects, such as a silica-microsphere, when excited with a laser under certain conditions, exhibit a set of optical resonances called as “whispering gallery modes” (WGMs). These modes are very sharp (high Q value) and can be harnessed as optical resonators. An interesting prospect is to channel the WGMs through a nanoscale plasmonic waveguide, such as a single silver nanowire, and study the optical emission.

Motivated by this prospect, Sunny Tiwari and Chetna Taneja from my group experimentally show how to channel WGMs through a plasmonic silver nanowire waveguide. They go a step ahead and show the spectral and angular characteristics of such a hybrid optical system. These experiments motivate further questions related to micro-resonances and angular spectrum distribution in dielectric-plasmonic hybrid systems, and can be harnessed to design compact micro-lasers and on-chip couplers. With some effort, they can also be optically trapped and manipulated.

arxiv link to the paper : https://arxiv.org/abs/2105.10698

DOI of the published paper: https://doi.org/10.1016/j.materresbull.2021.111412

41. New paper

A small thing to cheer during these gloomy times…

A new collaborative paper in Optics Express on modal and wavelength conversions in plasmonic nanowires

Work done by Adrian, Deepak K Sharma et al,
as part of Ifcpar Cefipra grant

We show that plasmonic nanowire-nanoparticle systems can perform nonlinear wavelength and modal conversions and potentially serve as building blocks for signal multiplexing and novel trafficking modalities. When a surface plasmon excited by a pulsed laser beam propagates in a nanowire, it generates a localized broadband nonlinear continuum at the nanowire surface as well as at active locations defined by sites where nanoparticles are absorbed (enhancement sites). The local response may couple to new sets of propagating modes enabling a complex routing of optical signals through modal and spectral conversions. Different aspects influencing the optical signal conversions are presented, including the parameters defining the local formation of the continuum and the subsequent modal routing in the nanowire.

Link to the paper: https://doi.org/10.1364/OE.421183

40. Tadashi’s practical application

Steven Strogatz is a well know applied mathematician from Cornell University, and has done some fascinating research on nonlinear dynamics (NLD). His lecture series on NLD and chaos is one of the best I have come across. Apart from writing columns in New York Times, he has also published some fantastic books on explaining mathematics, its relevance and impact on our daily lives, society and ecology.

Steve Strogatz has also been hosting The Joy of x podcast on the Quanta Magazine. In there, he interviews many contemporary mathematicians and scientists, who are actively involved in research and teaching. I found these informal interactions and exchange of ideas very interesting.

In one of the podcasts, Steven interviews Tadashi Tokieda, a mathematician who is interested in toys, and specifically the intriguing mathematics and physics of toys. In this interview, Tadashi describes his journey as an artist, philologist and as a professor who works on mathematics of toys.

Towards the end of the podcast (around 49 min in this audio), Tadashi describes how people (especially adults) ask him about the practical applications of studying toys, and how it can be beneficial to them. To this, his answer is something on the following lines :

When I show these toys to children, and explain to them the science and mathematics related to the toys, they feel very happy about it. What can be a better practical application that this !

Listening this just made my day…

39. Paper on nanophotonics of 2D material

We have a paper appearing in Advanced Photonics Research, in collaboration with the group of my colleague Atikur Rahman.

One of my PhD students, Shailendra Kumar Chaubey, is passionate about nanophotonics of 2D materials and its interface with plasmonic nano-elements. In collaboration with Atikur Rahman’s group, Shailendra, Gokul, Diptabrata Paul and Sunny Tiwari have experimentally shown directional photoluminescence from WS2 monolayer sandwiched between a plasmonic nanowire and a gold film.

Such directional emission is a vital step in photonic signal processing on a chip, and can serve as a solution-processed, soft platform to study optical emission in nonlinear and quantum optical regimes.

Personally, I am intrigued by the prospect of using optical trapping and assembly on such 2D materials to influence emission characteristics. Work is under progress in this direction…more on this later..

Link to the the arxiv version of the article is below

https://arxiv.org/abs/2103.01117

38. K.S. Krishnan et al., – students related to the discovery of Raman effect

Above picture : A group of 5 students of Raman. Front row- Left to Right 1) S. Vekateswaran, whose observations on the polarized ‘weak fluorescence’ of glycerine in early 1928 started the last lap of investigations which led to the discovery of the Raman effect. 2) K. S. Krishnan, he was 31 when this photograph was taken. 3) A. S. Ganesan – spectroscopist, later editor Current Science, who worked with Raman. He compiled the first bibliography of the Raman effect which Rutherford submitted to the Nobel Committee when he proposed Raman for the Nobel Prize. Back row. 1) C. Mahadevan, who later became renowned geologist who did his post-graduate work with Raman on X-ray studies of minerals. He was present at the Indian Association for the Cultivation of Science in Calcutta during the momentous discovery of the Raman effect and he has left graphic accounts of what happened then. Right S. Bhagavantam, another renowned student of Raman, who worked with him after the discovery of the Raman effect and is well-known for his application of group theory to the Raman effect. Reproduced from Current Science, Vol 75, NO. 11, 10 DECEMBER 1998

Today is National Science Day in India. We celebrate this day in commemoration of the discovery of the Raman effect. I have previously written about the significance of this day.

One of the important aspects of the discovery of the Raman effect is the role played by the then student K.S. Krishnan, who went on to be become a distinguished scientist and the founding Director of National Physics Laboratory, Delhi. There were also a few others who played a part in this discovery too (see picture)

Raman Research Institute has an excellent repository of the collected works of Raman. It also has a lot of content about Raman.

Of the many documents, the one which caught my attention was an interview of K.S. Krishnan by S. Ramaseshan, which was published in Current Science. Below I reproduce a few excerpts from the article:

“I (Ramaseshan) said there was a view that he (Krishnan) years discovered the Raman effect for Raman and this  view had again surfaced. His reply was ‘It is a blatant misrepresentation. The best I can say is that I participated actively in the discovery”

Krishnan goes on to say how it all started with Raman taking the initiative. In fact, Krishan vividly describes the scene :

‘The story starts in the early Febrauary 1928 when Professor (Raman) came to
my room and said “I want to pull out of the theoretical studies in which
you have immersed yourself for the 2 or 3 years. I feel it is not quite healthy
for a scientific man to be out of touch with actual experimentation and experimental facts for any length of time’

Interestingly, Raman and Krishan fell out of each other, and this interview has some snippets of this controversy. The article has some comments by S. Chandrasekhar on the credit of discovery behind Raman effect, in which he attributes Raman and Krishan’s collaborative approach towards the discovery, and mentions about the importance of exchanging ideas between two researchers working on a problem.

Overall, I must mention that the interview and the historical anecdotes in the document are riveting to say the least, and also showcases the complexity and sociology of a scientific discovery.

Science, per se, is objective. But pursuit of science has a human element, which makes it complex and interesting…

So always remember that as we commemorate the effect named after a person, but there are a few more people who have contributed to it. After all, science is a collective human endeavor.

Happy Science Day !

37. A call from Varanasi

Today (4th Feb, 2021), I had a strange but pleasant experience.

At around 5pm, I got a call on my office number from a person named Anil Tiwari from Varanasi. He told me that he had some questions related to science and he wanted to get some clarifications. Initially, I was a bit reluctant to engage in the conversation, as he was incoherent and probably a bit nervous. Then, he gradually gained some confidence, and mentioned that he was not convinced that the speed of light is a constant irrespective of the frame of reference in which it was measured, and he had difficulty in understanding the concept of light and its connection to electricity and magnetism. This led to our conversation on Maxwell’s electromagnetic theory and Michelson-Morley’s experiment to (dis)prove ether. I also urged him to look up history of light and Michelson’s lifelong obsession of measuring velocity of light. As our conversation went further, he mentioned that he wishes to understand the concept of light in its complete depth, and asked me for further references. I mentioned that he should read Feynman’s book on QED, and told him that Feynman’s explanation of interaction of light with matter was possibly one of the deepest understanding of nature we have.

All this conversation was in Hindi, and perhaps, my lengthiest attempt to talk science in that language. Then, Anil thanked me for the time I spent (around 10 to 15 min), and we were about to hang-up. Casually, I asked him how he could find my number, and he told me that he googled about light and matter, and he stumbled upon my webpage from which he could get the number. Then, I asked him if he was a student and where was he studying?  He hesitantly replied that he had completed his BSc many years ago, and now he was a farmer working in the fields, and was still interested in science. In order to spend time in the evening, it seems he watches science videos on YouTube and came across many interesting topics, of which velocity of light caught his attention recently, and he had many questions regarding this. I was elated to know about this, and strongly encouraged him to look up and study some good books including Feynman’s lectures and many other resources freely available on the internet.

Then we ended the call, and I could feel that both of us had an enjoyable conversation in science. Undoubtedly, this was a small but a pleasant experience for me, and reinforces my faith in science, in India, and importantly in humanity….