Groups | Seminars || Courses | Outreach


Seminars return this semester to room S-141 in the Physics and Astronomy Department building on Mondays at 11:00 AM, unless noted otherwise. When necessary, virtual seminar Zoom login instructions will be sent out via email.

Fall 2021

November 8, 2021

Prof. Luis A. Orozco
Joint Quantum Institute, UMD

Optical nanofibers: Some Experiments in Optomechanics

(Host: Tom Weinacht)

Optical nanofibers are produced by gradually reducing an ordinary single-mode optical fiber to half-micron diameters, less than the typical wavelength we use at 780 nm. We have studied the optomechanical coupling between the angular momentum produced by polarized light and the torsional mode one of those nanofibers. We have observed significant changes, decrease and increase, in the thermal noise of the fundamental torsional mode depending on the angle of polarization with respect to the apparent birefringence axes of the nanofiber. We measure the thermal noise reductions with the Maxwell Boltzmann distribution of amplitude fluctuations and show cooling by more than a factor of five from room temperature. This cooling happens to all the torsional modes and is free of any optical cavity, opening new avenues to optomechanical investigations.

November 15, 2021

Prof. Marissa Weichman
Princeton University

Molecules in Optical Cavities: Precision Spectroscopy & Strong Light-Matter Interactions

(Host: Tom Allison)

In this talk, I will discuss some of the major results from my postdoctoral work at JILA/CU Boulder, as well as new projects we are embarking on in the Weichman Lab, which launched in July 2020 at Princeton Chemistry.

Direct frequency comb spectroscopy is a sensitive, broadband, and precision technique that can be used to interrogate the quantum structure of unprecedentedly large molecular species. Frequency combs are light sources consisting of thousands of evenly spaced, sharp frequency “teeth.” Cavity-enhanced frequency comb spectroscopy (CE-FCS) matches a comb’s evenly spaced spectral structure to the resonant modes of a high-finesse optical cavity. This method allows for simultaneous detection of absorption signal across the comb spectrum, extremely high frequency resolution, and high sensitivity as the cavity enhances the interaction length between light and sample. We combined cryogenic buffer gas cooling of large molecules with CE-FCS in order to measure the rovibrational structure of buckminsterfullerene (C60), a molecule of great fundamental and astrochemical interest and a longstanding spectroscopic challenge. I will discuss the details of these measurements, which represent the first direct probe of the quantum state-resolved structure of C60 and establish it as by far the largest molecule for which a state-resolved spectrum has been reported.

For applications in cavity-enhanced spectroscopy, optical cavities enhance the strength of light-matter interactions and increase absorption sensitivity. The Weichman Lab’s future interests lie in a more exotic regime for intracavity molecules. The interaction of light and matter is typically weak and can be treated perturbatively. This picture breaks down in the regime of strong coupling, where the rate of light-matter interaction competes with the dissipation of excitations.  In this regime, Schrödinger’s cat-like superposition states with mixed light-matter character, dubbed polaritons, emerge. Polaritons inherit the coherent, wavelike nature of light while maintaining local molecular interactions and structure. Polaritonic molecules may therefore demonstrate distinct reactivity from their ordinary uncoupled counterparts, representing an extremely rich sandbox for new chemistry. I will discuss two new polariton chemistry projects we are starting at Princeton. We are setting out to build a detailed picture of how molecular polaritons behave and react, using ultrafast and precision spectroscopy to follow the reaction dynamics of benchmark condensed-phase and gas-phase systems under strong light-matter coupling.