Cavity-enhanced direct frequency comb spectroscopy

TL;DR

Cavity-enhanced direct frequency comb spectroscopy integrates broad bandwidth, high resolution, and ultrahigh sensitivity using an optical frequency comb and high-finesse cavity, enabling advanced spectroscopic measurements across various applications.

Contribution

This review details the principles, implementations, and applications of cavity-enhanced direct frequency comb spectroscopy, highlighting recent experimental advances and diverse cavity-comb coupling techniques.

Findings

Enhanced sensitivity for trace gas detection.

Successful human breath analysis using the technique.

Characterization of cold molecular beams with high precision.

Abstract

Cavity-enhanced direct frequency comb spectroscopy combines broad spectral bandwidth, high spectral resolution, precise frequency calibration, and ultrahigh detection sensitivity, all in one experimental platform based on an optical frequency comb interacting with a high-finesse optical cavity. Precise control of the optical frequency comb allows highly efficient, coherent coupling of individual comb components with corresponding resonant modes of the high-finesse cavity. The long cavity lifetime dramatically enhances the effective interaction between the light field and intracavity matter, increasing the sensitivity for measurement of optical losses by a factor that is on the order of the cavity finesse. The use of low-dispersion mirrors permits almost the entire spectral bandwidth of the frequency comb to be employed for detection, covering a range of ~10% of the actual optical frequency. The light transmitted from the cavity is spectrally resolved to provide a multitude of detection channels with spectral resolutions ranging from a several gigahertz to hundreds of kilohertz. In this review we will discuss the principle of cavity-enhanced direct frequency comb spectroscopy and the various implementations of such systems. In particular, we discuss several types of UV, optical, and IR frequency comb sources and optical cavity designs that can be used for specific spectroscopic applications. We present several cavity-comb coupling methods to take advantage of the broad spectral bandwidth and narrow spectral components of a frequency comb. Finally, we present a series of experimental measurements on trace gas detections, human breath analysis, and characterization of cold molecular beams.