High Duty Cycle Dual-Comb Spectroscopy*

Dual-comb spectroscopy is a relatively new technique that has revolutionized the field of spectroscopy by offering the unique advantage of high-resolution spectroscopy without the need for a moving mechanical part. The technique works by sending out femtosecond pulses of light from each laser, with the first laser (signal comb) probing the sample and exciting the electrons within the sample. The electron decay process is then measured using LO comb pulses that have a slightly different repetition rate. By analyzing the decay process, the technique provides highly precise information about the chemical composition and physical properties of the sample.

However, the current approach of dual-comb spectroscopy is significantly less effective (has the low duty cycle) if the decay process of the sample is much quicker than the time between the pulses.  For example, if one uses 100 MHz repetition rate lasers (10 ns spacing between the pulses) to probe samples with ~ 10 ps dephasing times, then the duty cycle will only be 0.1%. In this work we propose an approach that addresses this issue in dual-comb spectroscopy. In our approach repetition rates of both combs (signal and LO combs) are locked and they equal to each other. An interferogram is generated by scanning the locking phase of the signal comb.  This approach allows rapid scanning of the relative delay between the pulses only in the region where the signal is nonzero.

This material is based upon work supported by the National Science Foundation under Grant No. [2235597]