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


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….      

36. Science for…?

As student of science and as a practicing researcher one can always ask why should we do science?

If you look at this question from an utilitarian viewpoint, especially in times where vaccination is in the news (for right and wrong reasons), one does not need to give strong justifications for doing science. Its relevance is there to see in our lives and its impact is it ubiquitous.

So, do scientists always think about an application while doing science? The answer is : not always.

In fact many important discoveries and inventions in science, even those which turn out to have huge applications, were not envisaged with an application in mind.

An illustration of this aspect is beautifully communicated in the above video by Prof. P. Balaram, who is an excellent scientist at IISc, and also served as its director in the past.

I should mention that during my PhD course work days, I had the privilege of taking professor Balram’s molecular spectroscopy course in the molecular biophysics unit of IISc.

Being a student of physics I was introduced to the fascinating concepts of molecular spectroscopy from biophysics and biochemistry viewpoint. I learnt a lot about molecules, their stereochemistry and their interaction with light in this fantastic course. Even to date, when I think about chirality in the optical physics, some of the lessons learnt during this course has come extremely handy. Undoubtedly this was one of the best courses I have attended.

General advice, especially for students in physics, is in order to get a deeper intuition in physics it is good to study some fundamental aspects in chemistry and biology. For sure ones understanding of concepts such as chirality and symmetry is enriched if we look at these topics from the chemistry and biology viewpoint.

Similarly students of chemistry and biology can get a deeper insight into the structure and dynamics of molecules if they understand the nature of light in the context of polarization, phase and momentum etc.

After all the universe we live in does not discriminate between the disciplines we used to study it…

35. Water droplets on hot tawa

Dosa (dosae in Kannada) is one of the most relished dishes in India. An important prerequisite to prepare a good dosa is a hot pan, usually called as tawa.

Usually, just before the dosa batter is spread on the tawa, a few drops of water is sprinkled on this heated surface.

The video shows the dynamics of water droplets on a heated tawa at around 800 frames per second. Notice how the droplet expands, oscillates and evaporate….all at a very fast pace

Interestingly such fluid dynamics and oscillations can also be realized by heating a metal surface with a laser beam, which we do do in my lab. Of course, in such a situation, the laser heating is more localised and dynamics of the fluid is more complex, and importantly one can trap and optically manipulate colloids, nanoparticles and molecules, in such environments. More on this in a future blog..

34. Panoramic view

Panoramic view in cameras is a trick in stitching angle of images. To reveal the bending angle, you can take a panoramic shot with a known curvature in the foreground, as done in this case with the stairs of the cricket ground. Thereafter, you can compare the bending angles with a normal image of the same foreground. Folks from IISER Pune can easily guess that the panoramic angle in this image is around 180 degrees (actually slightly less than 180 degrees..)

32. Floating bubble…

Optics of bubbles and droplets is always fascinating to study. Above picture is of a floating soap bubble whose surface reflects the illuminating light source (in this case a single tubelight). Interesting questions: what determines the position and number of reflections ?

31. Fluctuating Sun..on a surface

In front of IISER Pune’s guest house, there is a small, artificial pond which is filled with rainwater. In there are tiny aquatic creatures and some beautiful lotus flowers. Recently, I happened to capture a high speed video (920fps) of the water surface fluctuating in this pond using the reflection of sun’s image (see video above). You will also notice a nice flower in the foreground which adds to the aesthetics.

What is interesting about this oscillation is the way the reflected image of the sunlight fluctuates as a function of time. In physics, there is a wonderful connection between fluctuating surfaces and the light reflected from such a surface. In principle, one can find out a lot about the nature of the fluctuation of the surface, including its topography, spatial frequency etc., by studying the amplitude and phase of the light that is reflected from such a moving surface.

One such example is the way atomic force microscope (AFM) works. In an essence, the topography of the surface an AFM reads, is by recording the fluctuation of light that is reflected from a tiny cantilever close to the surface.

Another fascinating concept related to probing fluctuations using light is the field of cavity optomechanics. The radiation pressure of the optical field couples to a tiny mechanical oscillator, and this interaction leads to a change in the the spectral characteristics of the light in a cavity. By studying this spectrum, one will be able to extract meaningful information about the tiny fluctuations in a cavity. This concept also applies to quantum fluctuations, and is one of the happening subfields in quantum optics and photonics.

Of course there are many such applications of using fluctuation of light to study oscillations in matter.

The model of simple harmonic oscillator that we study in physics is not only of basic relevance to understand any kind of fluctuation, but also applies to a variety of scientific processes in spatial, temporal and spectral domains. Added to this, if we learn about Fourier series and Fourier transforms, then we can go deeper in understanding fluctuations of any kind.

This reminds me of a quote attributed to Sidney Coleman:

The career of a young theoretical physicist consists of treating the harmonic oscillator in ever-increasing levels of abstraction.”

This is also true of experimental physics or for that matter most of the aspects of measurement science and technology. After all, fluctuations are ubiquitous, and harmonic oscillators are the windows into this beautiful world.