Optical frequency linked dual-comb absorption spectrum measurement

Abstract

Dual-comb spectroscopy is becoming a highlighted topic in broadband spectrum measurement techniques because of two outstanding advantages. One is its highly stable output frequency, which leads to an appealing resolution, and the other is the omitting of moving parts, which helps achieve extreme fast sampling rate. Utilizing the traditional radio frequency linked combs, however, obstructs the dual-comb spectroscopy reaching satisfied performance because the phase noise of the radio frequency standard causes the dual-comb mutual coherence to severely degrade. Specifically, traditional frequency comb stabilizes the carrier envelope offset at a radio frequency by a self-reference system, and the order number of each output comb tooth is over a hundred thousand. Thus, the phase noise of the radio frequency reference is significantly multiplied in output optical frequency by the same order of magnitude as the tooth order number. In this paper, we demonstrate an optical frequency linked dual-comb spectrometer where the two combs are locked to a common narrow linewidth laser. In this configuration, the two combs are synchronized at an identical optical frequency, which means that the carrier envelope offset of the two combs are changed to an optical frequency and the order number of the output comb teeth are reduced by two orders of magnitude. Therefore, not only the complex and costly self-reference system can be removed but also the phase noise of the optical frequency of each comb tooth is effectively reduced, which leads to lower mutual frequency jitters and better mutual coherence. To prove the performance, we measure the 1+3 P branch of 13C2H2 molecular and the results accord well with the reported line positions and reveals a spectral resolution of 0.086 cm-1. The average signal-to-noise ratio exceeds 200:1 (62.5 ms, 100 times on average) and the noise equivalent coefficient is 6.0106 cm-1Hz-1/2. This work provides a solution for pragmatic dual-comb spectroscopy with high resolution and low-cost configuration.