Tag: physics

Conversation with Aparna Deshpande

Welcome to the podcast, Pratidhavani – Humanizing Science

Aparna Deshpande is an Associate Professor of Physics at IISER Pune, specializing in atomic-scale exploration of two-dimensional materials and their interfaces using scanning tunneling microscopy. She is deeply engaged in research on nanomaterials and is active in physics education (as part of the department of science education at IISER Pune), communication, and outreach at IISER Pune.

Aparna is also the faculty in charge of the Smt. Indrani Balan Science Activity Centre at IISER Pune, where she leads diverse science outreach and STEM education initiatives, promoting hands-on multi-lingual learning and innovative workshops for students and teachers across India.

In this conversation, we explore her research in physics and science education.

You can also watch or listen on spotify

References:

[1] “Dr. Aparna Deshpande.” Accessed: Sept. 25, 2025. [Online]. Available: https://draparnadeshpande.github.io/portfolio/

[2] “Dr. Aparna Deshpande (@DrAparnaIISERP) / X.” X (formerly Twitter). Accessed: Sept. 25, 2025. [Online]. Available: https://x.com/draparnaiiserp

[3] “Aparna Deshpande | LinkedIn.” Accessed: Sept. 25, 2025. [Online]. Available: https://www.linkedin.com/in/aparna-deshpande-01927015/?originalSubdomain=in

[4] “Aparna Ramchandra Deshpande – Google Scholar.” Accessed: Sept. 25, 2025. [Online]. Available: https://scholar.google.com/citations?user=f5FnqMIAAAAJ&hl=en

[5] “Aparna Deshpande – IISER Pune.” Accessed: Sept. 25, 2025. [Online]. Available: https://www.iiserpune.ac.in/research/department/physics/people/faculty/regular-faculty/aparna-deshpande/259

[6] J. Poskett, Horizons. London, UK: Penguin Books, 2023. Accessed: Sept. 25, 2025. [Online]. Available: https://www.penguin.co.uk/books/313423/horizons-by-poskett-james/9780241986264

[7] P. Lockhart and K. Devlin, A Mathematician’s Lament. Illustrated ed. New York, NY: Bellevue Literary Press, 2009. https://www.blpress.org/books/a-mathematicians-lament/

Satish Dhawan – truly a man for all seasons

Image credit: Current Science 119, no. 9 (2020): 1427–32

Today is the birth anniversary of Satish Dhawan (25 September 1920 – 3 January 2002). He was probably India’s best scientist-administrator who headed institutions such as the Indian Institute of Science and the Indian Space Research Organization. With a PhD from Caltech, he came back to India and set up a marvellous research enterprise on fluid mechanics, including aerospace science and engineering. He mentored some of the outstanding scientists of India and led scientific institutions with vision, openness and informality, which is still a great benchmark to emulate1.

Below are a couple of historical documents related to Dhawan:

The first one is a lecture note from 1979, on making a case for a national satellite system and how it influences science and scientific activity (a copy of this note has been reproduced in a wonderful tribute to Satish Dhawan written by P. Balaram on his birth centenary2).

The next one is a beautiful perspective article written by Dhawan on ‘Bird Flight’ from an aerodynamics perspective3. It is a detailed overview of the dynamics of bird flight and shows Dhawan’s interest and ability to bridge two facets of science. It is a prototypical example of interdisciplinary research.

Finally, let me end the blog with a quote from P. Balaram on Satish Dhawan4:

“Dhawan mentored some remarkable students and built the discipline of aeronautical engineering at the Institute. He influenced aeronautical research and industry in India in a major way. He shepherded the Indian space programme following Vikram Sarabhai’s untimely death. He served the Indian scientific community in many ways. His stewardship transformed IISc. How then do we describe such a man? Dhawan studied English literature obtaining a Master’s degree in his youth. It may therefore be appropriate for me to borrow a 16th century description of Sir Thomas More:


‘[Sir Thomas] More is a man of an angel’s wit and
singular learning. I know not his fellow. For where is
the man of that gentleness, lowliness and affability?
And, as time requireth, a man of marvelous mirth and
pastimes, and sometime of as sad gravity. A man for
all seasons.’

Satish Dhawan was truly a man for all seasons.”

Happy Birthday to Prof. Satish Dhawan!

References:

  1. Current Science, in 2020, had a section of a volume dedicated to the birth centenary of Satish Dhawan, and has a foreword by his daughter and articles by many of his students and co-workers. https://www.jstor.org/stable/e27139029 ↩︎
  2. P. Balaram, “Satish Dhawan: The Transformation of the Indian Institute of Science, Bangalore,” Current Science 119, no. 9 (2020): 1427–32. This reference has many interesting references, including a handwritten obituary of CV Raman written by Dhawan https://www.jstor.org/stable/27139041. ↩︎
  3. S. Dhawan, “Bird Flight,” Sadhana 16, no. 4 (1991): 275–352, https://doi.org/10.1007/BF02745345. ↩︎
  4. P. Balaram, Current Science 119, no. 9 (2020), page 1432. https://www.jstor.org/stable/27139041. ↩︎

Leipzig – where Heisenberg worked…

From 16th to 18th Sept, 2025, I attended and gave a talk at Optofluidix 2025, thanks to the invitation of Prof. Frank Cichos and his team, Department of Physics, University of Leipzig.

This department is steeped in history, and this post is to give you a pictorial glimpse of some people who worked there.

Werner Heisenberg, aged 25, became a Professor at the University of Leipzig, Germany. It was an illustrious department then, had professors such as Peter Debye, Gustav Hertz (of the Franck-Hertz experiment fame), Friedrich Hund and many others. Felix Bloch was a student of Heisenberg in Leipzig.

As the AIP archives describe, “Only 25 years old in October 1927, Heisenberg accepted appointment as professor of theoretical physics at the University of Leipzig, Germany. Friedrich Hund soon joined his former Göttingen colleague as Leipzig’s second professor of theoretical physics. Heisenberg headed the Institute for Theoretical Physics, which was a sub-section of the university’s Physics Institute, headed until 1936 by the experimentalist Peter Debye. Each of the three professors had his own students, assistants, postdocs, and laboratory technicians.”

Below are a few snapshots that I took while visiting the department. Special thanks to Diptabrata Paul (my former PhD student and currently a post-doc in Cichos’ group) for showing me around the department.

Liquid Crystal Droplets + Plasmonic nanoparticle clusters

A droplet of liquid can act as an optical resonator. One can create a droplet of a liquid crystal and utilize its optical and topological properties. In recent times, liquid crystal droplets have emerged as a ‘soft photonic element’ in topological optics and photonics. Studying their optical behaviour in a controlled environment is a contemporary research problem.

In this context, we have an arXiv preprint on liquid crystal droplets and their reversible coupling to a small assembly of nanoparticles on a glass surface (see video).

Specifically, we ask: What happens to the modes of light inside the droplet due to such an interaction?

Thanks to the efforts of Sumant Pandey, we experimentally demonstrate the utility of optical tweezers to proximally couple (and decouple) nematic liquid crystal droplets to gold nanoparticle clusters, and record whispering gallery modes in coupled and decoupled states. We observe tuning of sharp resonant modes.
For more details, see the preprint: https://arxiv.org/abs/2509.10126v1

Art and Chu – in Bell labs

Steven Chu and Arthur Ashkin in 1986, in front of the apparatus shortly after the first optical trapping experiment was completed. Image from Chu’s Nobel lecture.

Steven Chu’s Nobel lecture has some gems. Below, he shares his experience of working with Arthur Ashkin.

“In 1986, the world was excited about atom trapping. During this time, Art Ashkin began to use optical tweezers to trap micron sized particles. While experimenting with colloidal tobacco mosaic viruses, he noticed tiny, translucent objects in his sample. Rushing into my lab, he excitedly proclaimed that he had ‘discovered Life’. I went into his lab, half thinking that the excitement of the last few years had finally gotten the better of him. In his lab was a microscope objective focusing an argon laser beam into a petri dish of water. Off to the side was an old Edmund Scientific microscope. Squinting into the microscope, I saw my eye lashes. Squinting harder, I occasionally saw some translucent objects. Many of these objects were ‘floaters’, debris in my vitreous humor that could be moved by blinking my eyes. Art assured me that there were other objects there that would not move when I blinked my eyes. Sure enough, there were objects in the water that could be trapped and would swim away if the light were turned off. Art had discovered bugs in his apparatus, but these were real bugs, bacteria that had eventually grown in his sample beads and water.”

Chu won the physics Nobel in 1997, and Ashkin won the same in 2018. Ashkin was the pioneer of optical trapping and tweezers, and applied it to a variety of problems, including the manipulation of biological matter. Chu harnessed the momentum of light to trap and cool atoms. Both started their work and collaborated at Bell Labs. Chu moved to Stanford, whereas Ashkin stayed back. Bell Labs was a remarkable place in the 1980s, as Chu describes in his lecture :

“Bell Labs was a researcher’s paradise. Our management supplied us with funding, shielded us from bureaucracy, and urged us to do the best science possible. The cramped labs and office cubicles forced us to rub shoulders with each other. Animated discussions frequently interrupted seminars and casual conversations in the cafeteria would sometimes mark the beginning of a new collaboration.”

Can the world afford to have another Bell Labs in 2025? Can it recreate the magic?

Real is imaginary and vice versa

This week in my optics class, I have been teaching Kramers-Kronig (KK) relations of electric susceptibility. It is fascinating to see the causality argument emerge from the relationship between the real and imaginary parts of the complex susceptibility. Whereas the time domain explanation is relatively easier to appreciate (that dissipation follows perturbation in time), for me, the frequency domain implication in KK relation is fascinating: the fact that information about the real part of the function at all frequencies can give you insight into the imaginary part at any given frequency (and vice versa) makes it such a powerful mathematical and physical tool. For example, by knowing the absorption spectrum of a medium, you can find out the refractive index of a medium at a particular frequency that is not easily accessible in experiments.

Two inferences I draw:

1) Complex analysis combined with differential calculus is one of the most beautiful and powerful mathematical tools invented, and exploring its application in experimental scenarios has made physics intriguing, useful, and profound.

2) The KK relationship shows how causality and the structure of matter are connected to each other, and by studying them, one will be able to extrapolate the idea beyond the problem at hand and apply it to a different context in physics. It just shows how ideas hop from one domain to another and how mathematics plays a critical role in intellectual arbitrage.

Real is imaginary and vice versa. Complex numbers zindabad!

When Chandra wrote to Hawking

Learning is a lifelong process, and even the best researchers have to update their knowledge as and when they come across new information. Subrahmanyan Chandrasekhar was undoubtedly one of the most accomplished mathematical astrophysicists in the 20th century, and his range of topics covered almost all aspects of astrophysics.  Chandra (as he was known) was a lifelong learner, and took up new topics within astrophysics, researched them deeply, and wrote definitive books on them, which are still of great utility even today. In his research process, Chandra consulted various scholars across the world, irrespective of their age, and learned new things.

In 1967, Chandra, aged 57, wrote a letter to a 25-year-old researcher, Stephan Hawking, to learn more about his work ‘on the occurrence of singularities in cosmology’. In this letter, which is written in a desperate tone, Chandra mentions that he is grappling with some mathematical aspects of Stephen Hawking’s work and is asking him for references that he can consult to understand his papers. Chandra describes reading Hawking’s papers as  ‘climbing a staircase moving downwards’. Below, I reproduce the letter (from the University of Chicago archives).

 To this letter, Hawking dutifully replies (see below), suggesting specific books on topology and differential geometry. Hawking also suggests some of his published papers. Hawking himself downplays his knowledge of mathematical aspects related to the work, and mentions that it improved after he consulted the mentioned books. Below, I reproduce the handwritten letter (from the University of Chicago archives).

There are two aspects that are interesting to note:  one is the fact that even accomplished researchers have to learn and relearn many things as they get exposed to new information, which calls for humility and setting aside egos, and the second aspect is that ideas are built on existing ideas available at that time, and a major part of it is to learn from papers, books and of course communicating with people, as Chandra did in this case.

Science, after all, is a human endeavor.

Conversation with Arka Banerjee

Welcome to the podcast Pratidhavani – Humanizing Science

Arka Banerjee is a cosmologist and an Assistant Professor of Physics at IISER Pune. His research focuses on exploring the connections between fundamental physics at microscopic scales and the formation and evolution of large-scale structures in the Universe, such as galaxies and cosmic voids. To pursue these questions, he develops new simulation methods, constructs summary statistics for cosmological data, and generates forecasts for upcoming observational surveys.

In this episode, we explore his intellectual journey and research.

Spotify link

References:

“Arka Banerjee – Home.” n.d. Accessed August 23, 2025. https://arkabanerjee.github.io/.

“‪Arka Banerjee‬ – ‪Google Scholar‬.” n.d. Accessed August 23, 2025. https://scholar.google.com/citations?user=kLde9gcAAAAJ&hl=en.

“Arka Banerjee – IISER Pune.” n.d. Accessed August 23, 2025. https://www.iiserpune.ac.in/research/department/physics/people/faculty/regular-faculty/arka-banerjee/381.

“Arka Banerjee – INSPIRE.” n.d. Accessed August 23, 2025. https://inspirehep.net/authors/1671323.

Some Optical and IR observatories in India

Below are ‘locations of some of the optical and infrared observatories marked on the Indian map’.

from: Narendranath, Shyama, Shashikiran Ganesh, Dipen Sahu, et al. 2025. “Solar System Research Prospects for the Decade and Beyond.” Journal of Astrophysics and Astronomy 46 (2): 34. https://doi.org/10.1007/s12036-025-10060-0.