Cavity-enhanced frequency comb spectroscopy of complex molecules

Precision spectroscopy has proved essential to uniquely assign molecular fingerprints in complex environments including Earth’s atmosphere and interstellar space; to inform molecular state preparation and control for applications in quantum information science; and to benchmark state-of-the-art quantum chemistry methods. While detailed spectroscopy is now routine for small molecules, resolving individual quantum states becomes a challenging endeavor on the brink of treatment with our current toolkit for systems with 50 or more atoms. Achieving a detailed picture of the quantum dynamics of molecules of transitional, nanoscale size is therefore a major frontier in experimental physical chemistry. Our lab is advancing this frontier by harnessing laser spectroscopy and molecular cooling methods from the atomic, molecular, and optical physics community.

Detailed spectroscopy of large, gas-phase molecules demands a method with (a) excellent frequency resolution, so measurement of narrow, closely spaced features is never instrument limited; (b) extremely high sensitivity, for detection of trace species and weak features; (c) broadband readout, allowing detection at many wavelengths simultaneously; and (d) rapid acquisition times to enable detection of transient species and minimize noise. Optical frequency comb lasers are the only existing technology that can simultaneously meet these demands. The spectra of these light sources consist of thousands of narrow, evenly spaced “comb teeth,” essentially acting as many thousands of individual stable lasers lasing synchronously. In cavity-enhanced frequency comb spectroscopy (CE-FCS), we match a comb’s spectral lines to the resonant modes of an optical cavity containing the absorber of interest. The cavity dramatically increases the pathlength of light through the sample, yielding highly sensitive absorption spectra capable of capturing weak features or trace species.  Our lab is developing a first-of-its-kind rapid-acquisition cavity-enhanced frequency comb spectrometer working in the long-wave infrared.

Our research interests lie in large part in laboratory astrochemistry: the detection of new astrochemical species is key to understanding the chemical underpinnings of star, planet, and galaxy formation and the origins of prebiotic molecules. We are targeting quantum-state-resolved spectroscopic studies of fullerenes and polycyclic aromatic hydrocarbons to aid in the identification of these species in observational data. Our effort is well-timed with the advent of the James Webb Space Telescope, which is conducting infrared campaigns with broader spectral coverage and orders-of-magnitude better sensitivity and spatial resolution than existing observatories. In parallel, our work will establish new records in the complexity and size of molecular systems that can be examined with complete quantum state resolution.

Current Project Members

Dr. Dominik Charczun
Negar Baradaran
Tanay Nambiar

Recent Publications