I am always amazed to see fractal-like patterns….this one at a geographical scale…captured somewhere over south India..
I took the photo on my trip back to Pune from IIT Madras…
Thanks to IIT-M physics department for their invitation for colloquium…
Special thanks to Basudev Roy and Nirmala for hosting…. greatly enjoyed the discussion with many faculties and students..
In my talk, I mainly spoke on topics at the interface of statistical optics, Brownian motion and pattern formation.. Was delighted to see (and meet) Profs. Balki, Suresh Govindarajan Sunil Kumar Arnab Pal and many more in the audience.
The photo, retrospectively, captures the essence of the science discussed…
About 2 years ago (22nd May 2020), when all the academic activities were online, I gave a talk on “Soft-Matter Optics: A Cabinet of Curiosities” organized by American Chemical Society as part of India Science Talks. Below is the embedded video of the online talk.
In there, I give a broad overview of how interesting optical function can emerge from the complex world of soft matter. In addition to this, I have emphasized how optics can be harnessed to study structure and dynamics of soft-matter systems including colloids, liquid crystal and some biological matter. The target audience are new PhD students and anyone who is entering the field of light-soft matter interaction.
I mainly spoke about emergent Brownian dynamics of laser-heated colloids under optical confinement. Below is the link to the talk.
I concluded my talk quoting P W Anderson’s essay “More is Different“
“The constructionist hypothesis breaks down when confronted with the twin difficulties of scale and complexity. The behavior of large and complex aggregates of elementary particles, it turns out, is not to be understood in terms of a simple extrapolation of the properties of a few particles.
Instead, at each level of complexity entirely new properties appear, and the understanding of the new behaviors requires research which I think is as fundamental in its nature as any other.”
P.W. Anderson ‘More is Different’ Science, 177, 4047 (1972)
M. Visvesvaraya was a legend and an inspiration… he was truly one of the makers of modern India…below is the link to his professional autobiography, available online for free
Memoirs of my working life. by Visvesvaraya, M (1951)
On 1st Dec 2022, I gave a talk on “Structured-Light Scattering : Implications in Momentum Space” as part of a discussion meeting on STRUCTURED LIGHT AND SPIN-ORBIT PHOTONICS held at International Center of Theoretical Sciences, Bangalore.
I mainly spoke about topological light scattering in the frame work of angular momentum of light and absorptive effects in optothermal tweezers created by structured light.
Below is the embedded video link to my talk. The playlist also has many other interesting talks related to the topic.
Appended is a link to arxiv preprint of an invited review article that I wrote as part of a special issue on nanophotonics in the Indian Journal of Physics and Applied Physics. The issue is edited by Dr. Achanta Venugopal (TIFR/NPL).
In this review, I discuss about assembly and dynamics of plasmonic colloids under the influence of optical vortex fields.
The abstract reads : Structured light has emerged as an important tool to interrogate and manipulate matter at micron and sub-micron scale. One form of structured light is an optical vortex beam. The helical wavefront of these vortices carry orbital angular momentum which can be transferred to a Brownian colloid. When the colloid is made of metallic nanostructures, such as silver and gold, resonant optical effects play a vital role, and the interaction leads to complex dynamics and assembly. This brief review aims to discuss some recent work on trapping plasmonic colloids with optical vortices and their lattices. The role of optical scattering and absorption has important implications on the underlying forces and torques, which is specifically enunciated. The effect of spin and orbital angular momentum in an optical vortex can lead to spin-orbit coupling dynamics, and these effects are highlighted with examples from the literature. In addition to assembly and dynamics, enhanced Brownian motion of plasmonic colloids under the influence of a vortex-lattice is discussed. The pedagogical aspects to understand the interaction between optical vortex and plasmonic colloids is emphasized.
Below is some basic advice I shared with my undergraduate class (Physics majors/Optics). This may be useful to other students here.
Do not copy a text verbatim, unless you are quoting the text as it is, with reference at that location. If you use a source, then write a summary in your own words and cite the original source at the location of your text.
In the absence of primary data (which you generate originally), you will be using secondary sources such as research papers, books and internet content. For scholarly purposes (including assignments), it is better to use journal articles and books as references. Wikipedia is essentially a tertiary reference. Although some entries are good, wikipedia content is generally taken from a book or a research paper. Identify that source and use it for your assignment and reference. Directly citing wikipedia (which is usually not peer reviewed by experts) is not a general practice in scientific literature.
When you take a figure or equation from a secondary resource (paper, book, internet), it is important that you cite the source in figure caption/equation location.
In an assignment, I am mainly interested in reading what you think about the topic under consideration. Feel free to put down your thoughts and compare and contrast it to the literature you use. This is where the thinking + learning happens.
For some general advice on referencing, especially for online communication, have a look at my blogpost.
To appreciate importance of written communication in learning, have a look at another blogpost.
We have a new paper to be published in ACS Photonics on “Optothermal evolution of active colloidal matter in defocused laser trap”
In the context of non-equilibrium statistical mechanics, it is relevant to ask : how does a system of (active) Brownian particles respond to environmental cues ?
Structured light in the form of an optical trap can facilitate a platform to create unconventional, environmental cues in which Brownian particles can dynamically assemble and evolve as a function of space and time.
In this work, we utilize a simple defocused laser trap and study the evolutionary dynamics of thermally active colloids (polystyrene spheres infused with iron oxide). We observe a variety of (nonlinear) dynamical states including hovering of a pair, a kind of synchrony among the assembled colloids in the trap (see video).
Thanks to the great efforts of Dipta and Rahul from my group, we have been able to study and unveil the complex forces at play. The dual contribution of optical potential of the laser and thermophoretic interaction of colloids were revealed by systematic experiments and numerical simulations leading to this elaborate report.
This study further motivates interesting questions in the context of microscopic heat engines where the light and heat created in an optical trap can lead to some interesting nonlinear dynamics of soft matter systems. Another prospect is to characterize structured optothermal fields using Brownian motors as microscopic probes in an optical trap. More on this in the coming month….
“While the focus is on the specific controversies listed in the table of contents, an even more valuable contribution of the book is the description of Roth’s methodology. In describing his approach to evaluating the science (or lack thereof) behind each claim, you will learn some of the thought processes needed to evaluate any new technology. Anyone who adopts these approaches will become a better investigator of new claims”
I have been following book-reviews of American Journal of Physics There are some really good recommendations and assessments.
VISMAYA - History & Philosophy of Physics 