Cavity-Enhanced Direct Frequency Comb Spectroscopy

Abstract

In less than fifteen years since the development of the first optical frequency comb (OFC), the device has revolutionized numerous research fields. In spectroscopy, the unique properties of the OFC spectrum enable simultaneous acquisition of broadband spectra while also providing high spectral resolution. Due to the regular structure of its spectrum, an OFC can be efficiently coupled to an optical enhancement cavity, resulting in vastly increased effective interaction length with the sample and absorption sensitivities as low as 1.3×10−11 cm−1 Hz−1/2 per spectral element. This technique, called cavity-enhanced direct frequency comb spectroscopy (CE-DFCS), provides ultra-sensitive absorption measurements simultaneously over a wide spectral range and with acquisition times shorter than a second. This chapter introduces the main ideas behind CE-DFCS including properties of various comb sources, methods of coupling and locking the OFC to the enhancement cavity, and schemes for broadband, simultaneous detection. Examples of experimental implementations are given, and a survey of applications taking advantage of the rapid, massively parallel acquisition is presented.