Soft Matter Physics + Photonics – my renewed interest

  Malleshwaram is one of the oldest parts of Bangalore. I studied BSc (Physics, Maths, Electronics) in MES College which is at the 15^th cross of Malleshwaram. Apart from the college day memories of eating Dosae at CTR, other memorable aspects of my student life were playing cricket at Malleshwaram ground, and regularly visiting IISc and Raman Research Institute (RRI), which were not far from Malleshwaram. Particularly, the library at RRI was the place I spent most of my time during BSc and MSc. Two Professors at RRI with whom I interacted a lot were Prof. G.S. Ranganath and Prof. G. Srinivasan (both are retired now). I owe a lot of my interest in science to these two gentlemen. I was always interested in optical physics, and thanks to the interaction with Prof. G Srinivasan, I really got interested in optical phenomena in astronomy and astrophysics (I even did a rotation curve experiment using the radio telescope at RRI).

      Thanks to this excitement, during my MSc Physics at Bangalore University, I did my summer research project at Indian Institute of Astrophysics, Bangalore with Prof. K.N. Nagendra, who introduced me to solar astrophysics. In fact, my project was on second solar spectrum and polarization of light in stars such as sun. Gradually, as I learnt more about optics in stellar environment, I increasingly became interested in optics of everyday life, and started exploring optics of rainbow, soap bubbles and other common objects.

 Concomitantly, during BSc and MSc days, I and some of my classmates used to visit RRI and interact with Prof. G.S. Ranganath. He was the one who introduced us to soft-matter physics. Importantly, he impressed upon me the fascinating world at the interface of soft-matter physics and optics. I strongly recommend one of his books, which discusses some of these topics.

 This introduction to soft-matter physics and interactions with Prof. Ranganath has had a profound impact on my research career.  So much so, that I joined Prof. Chandrabhas’s lab at JNCASR for my Ph.D. to work on a (then) newly emerging topic of surface enhanced Raman scattering, which had a unique blend of colloids (a prototypical soft-matter) and light scattering, and it perfectly suited my research interest. During my Ph.D., I had a fantastic and thrilling experience of working on topics related to interaction of metal colloids with biological macromolecules using Raman scattering microscope as a tool. Thanks to the deep knowledge of Prof. Chandrabhas on optics and optical spectroscopy, and a variety of research at JNCASR, I got introduced to the fascinating field of optical microscopy, Raman scattering and soft-matter physics. Then during my post doc, first at ICFO-Barcelona, I got introduced to near-field optics and single-molecule imaging, and then at Purdue University, I learnt a bit of cell biology and used plasmonic light scattering to study some questions in bio-imaging.

Ever since I started my own research group in 2010 at IISER-Pune, my research interest evolved in topics such as nanowire plasmonics, spin and orbital angular momentum of light, whispering gallery modes in microspheres, single-molecule Raman scattering, and Fourier-plane optical microscopy and spectroscopy.  As of Feb 2020, 6 Ph.D. students and around 9 MS students have graduated working on the abovementioned topics. The main focus, for about 10 years, has been on nanophotonics, and on some topics related to soft-matter physics, especially on colloids.

Starting Jan 2020, our emphasis and research orientation will be mainly towards ‘soft-photonics’.  The motivation of this research is to explore some emerging questions at the interface of soft matter physics and micro- and nano-photonics. There are two important objectives to this research:

• To study structure and dynamics of mesoscale soft-matter including colloids, liquid crystals, and complex fluids using a variety of techniques that we have developed for the past 10 years in the area of nanophotonics and single-nanoparticle optics.
• To explore new opportunities in meso- and nano-photonics using soft-matter systems such as colloids, liquid crystals, droplets and bubbles, as a platform.

In a way, for the past 5 years or so, we have been implicitly working on these objectives. But from 2020 onwards, we will be mainly focusing on these objectives, and will be orienting all our efforts towards this direction.

 This explicit reorientation is for the following reasons:

• The interface of soft-matter physics and photonics provides some new opportunities to study some interesting questions in fundamental physics (such as topology, pattern formation, emergence and single-macromolecule dynamics) and applications (optofluidics, optical antennas, aerosol optics and gastronomy)
• Light scattering and “quantitative” optical microscopy have emerged as powerful tools to study structure and dynamics of soft-matter. Given that our lab has laid a strong foundation in these tools for 10 years or so, it is an obvious extrapolation of our capabilities.
• Thanks to the interaction with my soft-matter colleagues at IISER-Pune and many friends/researchers across India and outside, I have been “re-hooked” to soft matter physics. Given that the Indian research community on soft-matter is growing in number and has a good mix of experiments and theory, further motivates me to pursue this direction.
• Perhaps the most important reason is that it renews my interest in science and reminds me of the fundamental reason of why I became a researcher: to enjoy what I do!

As a consequence of this renewed interest, I intend to write blogs oriented towards soft matter physics + photonics and wish to use this platform to educate myself and communicate my excitement with all of you.

Let me conclude by quoting “a poem from an experiment of soft matter” by Boudin, which is also the concluding part of the Nobel lecture of Pierre de Gennes:

“Have fun on sea and land

Unhappy it is to become famous

Riches, honors, false glitters of this world

All is but soap bubbles”