47. Nagendra, Weinberg and some memories…

IIA days…

It was late summer/early monsoon season of 2003, in Bangalore. The BTS bus travel from Rajajinagar to Koramangala via Majestic used to take 90 min or more. This commute, which I did for about 2 to 3 months, as summer student at Indian Institute Astrophysics (IIA) is still etched in my memory. I had just finished my first year MSc (Physics), and was seriously hooked on to physics in general, and astrophysics in particular. My summer project was on second solar spectrum guided by Prof. K. N. Nagendra (KNN) at IIA. It was he who introduced me to the fabulous world of polarization optics in the context of solar physics. This opened my eyes to the spectacular world of photon transport through an inhomogeneous medium, and hence multiple scattering of light. It was KNN who also introduced me to the classic : Radiative Transfer by Subrahmanyan Chandrasekhar. My first task as a summer student was to read the first chapter of this book and understand the representation of polarized light using Stokes parameters. The summer of 2003, was also the first time I encountered the power of computational methods to solve scientific problems, and ever since then I have deeply appreciated the role of computers in solving scientific problems. This introduction to computational physics and polarization optics (in the form of Jones, Stokes and Muller matrices) has turned out to be an important concept which I still use in my research. I thank KNN for this.

Recently, I was shocked to know that Prof. KNN passed away. His death was untimely, and a very sad news to me and many of the people who knew him. My condolences to his family, friends and students.

Weinberg inspires…

Recently, I also came to know about the sad demise of Steven Weinberg. Thanks to a special paper on Introduction to Quantum Electrodynamics in the final semester of my MSc, I learnt a bit about Weinberg as we were introduced to some aspects of unification of weak and electromagnetic forces. Also, with great enthusiasm, I learnt a lot from his fascinating book : The First Three Minutes: A Modern View of the Origin of the Universe. Undoubtedly, the scientific world has lost a great thinker.

The greatest impact of Weinberg on me was in a different context. In summer of 2004, I was selected for a PhD position at JNCASR. Prof. Chandrabhas had agreed to take me in as a PhD student, and I was elated and excited to join his group. I still remember the first time I visited his lab (after the selection) sometime in late May or early June 2004. As I entered the lab and opened that famous sliding door, there was a print-out of an article which was pasted right beside the door. This article was the Four Golden Lessons by Steven Weinberg, which was then recently published in 2003. This was literally, the first article I read as a PhD student in the lab, and has deeply impacted my work.

I still revisit the four golden lessons, time and again, and has been extremely useful throughout my career. As a tribute to him, below I reproduce the third lesson, which I think is worth contemplating :

My third piece of advice is probably the hardest to take. It is to forgive yourself for wasting time. Students are only asked to solve problems that their professors (unless unusually cruel) know to be solvable. In addition, it doesn’t matter if the problems are scientifically important — they have to be solved to pass the course. But in the real world, it’s very hard to know which problems are important, and you never know whether at a given moment in history a problem is solvable. At the beginning of the twentieth century, several leading physicists, including Lorentz and Abraham, were trying to work out a theory of the electron. This was partly in order to understand why all attempts to detect effects of Earth’s motion through the ether had failed. We now know that they were working on the wrong problem. At that time, no one could have developed a successful theory of the electron, because quantum mechanics had not yet been discovered. It took the genius of Albert Einstein in 1905 to realize that the right problem on which to work was the effect of motion on measurements of space and time. This led him to the special theory of relativity. As you will never be sure which are the right problems to work on, most of the time that you spend in the laboratory or at your desk will be wasted. If you want to be creative, then you will have to get used to spending most of your time not being creative, to being becalmed on the ocean of scientific knowledge. (emphasis is mine)

Thank you, KNN and Weinberg…for some golden lessons…

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 choas 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 !