Vacuum Ultraviolet Dual-Comb Spectroscopy

TL;DR

This paper demonstrates vacuum ultraviolet dual-comb spectroscopy using intracavity high harmonic generation, enabling precise measurements of molecular spectra at challenging wavelengths with high accuracy and resolving complex spectral features.

Contribution

It introduces a novel dual-comb spectroscopy technique in the vacuum ultraviolet region using intracavity high harmonic generation, expanding the accessible spectral range.

Findings

Measured molecular spectra at 210 nm and 149 nm from acetylene and ammonia.

Resolved Doppler-broadened spectral structures with high frequency accuracy.

Characterized noise sources to inform future technological improvements.

Abstract

The optical frequency comb has made a significant impact in precision spectroscopy and on our ability to probe atomic, molecular and, recently, nuclear transitions to further our understanding of their fundamental properties and how their dynamics and complex interactions affect the observed world. To expand the energy scales and types of systems that can be studied, frequency comb sources from terahertz to vacuum ultraviolet frequencies and beyond have been pursued. Dual-comb spectroscopy, enabled by the development of these frequency comb sources, allows broadband absorption measurements of complicated spectra, exceeding the limitations of direct, single-comb spectroscopy. To date, however, the dual-comb approach has not been able to directly access many important transitions that lie at challenging vacuum ultraviolet wavelengths. Here, we demonstrate dual-comb spectroscopy in the vacuum ultraviolet utilizing intracavity high harmonic generation. This multi-harmonic source is used to measure molecular absorbance spectra at $\lambda=210$~nm and $\lambda=149$~nm from room-temperature samples of acetylene and ammonia, respectively. These measurements resolve the Doppler broadened structure of congested molecular spectra with absolute frequency accuracy. Noise contributions to the vacuum ultraviolet dual-comb spectroscopy measurements are characterized, guiding future efforts and technological development in this region.