# Doppler-free laser spectroscopy of buffer gas cooled molecular radicals

## TL;DR

This paper presents a Doppler-free laser spectroscopy method for cold molecular radicals, enabling high-resolution spectral analysis of difficult-to-produce molecules at controlled temperatures.

## Contribution

The authors develop a technique combining buffer gas cooling and Doppler-free spectroscopy to study molecular radicals with high resolution and temperature control.

## Key findings

- Achieved 30 MHz resolution in YbF radicals
- Measured magnetic hyperfine parameters accurately
- Demonstrated method's applicability to various molecules

## Abstract

We demonstrate Doppler-free saturated absorption spectroscopy of cold molecular radicals formed by laser ablation inside a cryogenic buffer gas cell. By lowering the temperature, congested regions of the spectrum can be simplified, and by using different temperatures for different regions of the spectrum a wide range of rotational states can be studied optimally. We use the technique to study the optical spectrum of YbF radicals with a resolution of 30 MHz, measuring the magnetic hyperfine parameters of the electronic ground state. The method is suitable for high resolution spectroscopy of a great variety of molecules at controlled temperature and pressure, and is particularly well-suited to those that are difficult to produce in the gas phase.