Category: optics

Gerhard Herzberg – scientific life


References:

Pavan Kumar, G. V. “Gerhard Herzberg (1904–1999): A Pioneer in Molecular Spectroscopy.” Resonance 29 (2024): 1339. https://www.ias.ac.in/describe/article/reso/029/10/1339-1345.

Stoicheff, Boris. Gerhard Herzberg: An Illustrious Life in Science. Ottawa : Montréal ; Ithaca N.Y.: Canadian Forest Service,Canada, 2002.

Stoicheff, Boris P. “Gerhard Herzberg PC CC. 25 December 1904 – 3 March 1999.” Biographical Memoirs of Fellows of the Royal Society 49 (December 2003): 179–95. https://doi.org/10.1098/rsbm.2003.0011.

Optothermal revolution – preprint

We have an Arxiv preprint on how a mixture of colloids (thermally active + passive particles in water) can lead to the emergence of revolution dynamics in an optical ring trap (dotted line). Super effort by our lab members Rahul Chand and Ashutosh Shukla.

Interestingly, the revolution emerges only when an active and a passive colloid are combined (not as individuals) in a ring potential (dotted line)

the direction (clock or anti-clockwise) of the revolution depends on the relative placement of the colloids in the trap

This revolution can be further used to propel a third active colloid

There are many more details in the paper. Check it out: https://arxiv.org/abs/2409.16792

Election in Pune and Zero shadow day

Today is election day in Pune (Lok Sabha), and I voted.

Today is also a ‘zero shadow day’ in Pune. The sun is exactly over our head (zenith), and no angle is subtended by the shadow. In the pic, the sun is captured at its zenith.

Caution: don’t look at the sun directly. This image was captured wearing filtered glass

Check the webpage of the Astronomical Society of India linked below. It has some good explanations and geographical locations in India where zero shadow day is observed.

Zero Shadow Day

Music beats on a metal water can

If you have a metal water can, what do you do ?…well make a geeky music video🙂

I played the water can to generate beats & recorded the response.

You will see the periodic beats + colour-coded audio-visualisation. 📹

Enjoy !

#fun #experiment

A metal water can was played to generate music beats, and the acoustic response was recorded. You will see the periodic beats in the timeline and a colour-coded audio-visualisation of it. Enjoy !

Graviton modes in solids: Old Argentinian wine in new Bottle ?

Recently, there has been a buzz about a Nature paper titled Evidence for chiral graviton modes in fractional quantum Hall liquids. There has been some media reportage on the paper too.

The paper makes interesting claim on observation of ‘chiral graviton modes’ in certain ultra-cooled semiconductors (Gallium Arsenide – famously called GaAs). The cooled temperature is quite low (~50 mK), which is impressive, and the chirality of the mode is unveiled using polarization-resolved Raman scattering. The observation of this so-called ‘Graviton modes’ is essentially a quasiparticle excitation, and has created some buzz. In my opinion, graviton-like behavior is a bit of an exaggeration.

Anyway, this paper has set an interesting discussion among my colleagues (condensed matter and high energy physics) in our department. To add to their discussion, I wrote on 2 points (and an inference) from optics perspective, which I am sharing below :

  1. The measurement scheme used to unveil the chirality of the quasi-particles is a well-known trick in polarization optics. In fact, I teach it to our undergrads. Notice the use of quarter-wave plates (indicated by the arrow in the figure below). This is also the measurement at the heart of unveiling optical anisotropy. Experimentally, what is impressive is the ultra-low energy excitation captured via Raman scattering. This is again thanks to the excellent cooling of the sample (50 mK).
Figure from the Nature paper.

2. The last author of this paper, Aron Pinczuk, was a well-known expert in light scattering in solids. He was an Argentinian-American professor at Columbia University, and passed away in 2022.

Aron Pinczuk

He and the legendary Manuel Cardona were instrumental (pun intended) in laying the foundation for using inelastic light scattering methods in solids. The first edition of the series “Light Scattering in Solids”, written in 1976, has Pincuk discussing the very measurement scheme used in the paper (see picture).  

The first edition (1976) of a great series : Light Scattering in Solids

My initial inference on the paper : This is an old Argentinan wine of quasiparticles in a new GaAs bottle at ultra-low temperature….and NATURE is selling it as champagne de graviton made in China !