Rapid, Broadband, Optical Spectroscopy of Cold Radicals

TL;DR

This paper introduces a rapid and efficient optical spectroscopy method for cold molecular radicals, combining a supercontinuum laser, cryogenic buffer gas source, and spectrometer to achieve high-resolution, broadband measurements with significantly increased throughput.

Contribution

The authors develop a novel, simplified setup that enables fast, high-resolution optical spectra measurement of cryogenically cooled radicals across broad bandwidths, improving efficiency over traditional methods.

Findings

Measured hundreds of spectral lines in a few hours

Achieved 15 nm bandwidth with 0.56 pm resolution

Successfully assigned molecular constants for multiple bands

Abstract

Optical spectroscopy of molecular radicals is an important tool in physical chemistry, and is a prerequisite for many experiments which use molecules for quantum science and precision measurement. However, even the simplest molecules have complex spectra which can be very time consuming to measure. Here we present an approach which offers the ability to measure the optical spectra of cryogenically-cooled molecular radicals with much greater efficiency. By combining a supercontinuum laser with a cryogenic buffer gas molecular source and a commercial optical spectrometer, we realize 15 nm of simultaneous bandwidth with 0.56 pm $(\approx 0.5$ GHz) resolution and high sensitivity. As a demonstration we measure and assign hundreds of lines and dozens of molecular constants from 15 bands in the $B^2\Sigma^+-X^2\Sigma^+$ system of CaF, including a low-abundance isotopologue, in a few hours. The setup is robust, simple, and should enable spectroscopy of molecular radicals with much higher throughput.