Linear and Nonlinear Time- and Frequency-Domain Spectroscopy with Multiple Frequency Combs

TL;DR

This paper compares and extends optical frequency comb spectroscopy techniques, demonstrating how multiple combs and ultrafast pulses can rapidly and accurately measure linear and nonlinear material susceptibilities in time and frequency domains.

Contribution

It introduces a multi-dimensional dual comb approach and relates it to ultrafast pulse sequences for enhanced nonlinear susceptibility measurements.

Findings

Multi-dimensional dual comb spectroscopy enables rapid susceptibility acquisition.

Ultrafast pulse sequences can recover nonlinear interaction pathways.

Both techniques effectively map high optical frequencies into detectable low-frequency signals.

Abstract

Two techniques that employ equally spaced trains of optical pulses to map an optical high frequency into a low frequency modulation of the signal that can be detected in real time are compared. The development of phase-stable optical frequency combs has opened up new avenues to metrology and spectroscopy. The ability to generate a series of frequency spikes with precisely controlled separation permits a fast, highly accurate sampling of the material response. Recently, pairs of frequency combs with slightly different repetition rates have been utilized to down-convert material susceptibilities from the optical to microwave regime where they can be recorded in real time. We show how this one-dimensional dual comb technique can be extended to multiple dimensions by using several combs. We demonstrate how nonlinear susceptibilities can be quickly acquired using this technique. In a second class of techniques, sequences of ultrafast mode locked laser pulses are used to recover pathways of interactions contributing to nonlinear susceptibilities by using a photo-acoustic modulation varying along the sequences. We show that these techniques can be viewed as a time-domain analogue of the multiple frequency comb scheme. %We compare the two techniques: in both, an optical high frequency is mapped into a low frequency modulation of the signal that can be detected in real time.