Measurement of absorption spectroscopy enabled by a polarization-multiplexed dual-comb laser

Abstract

Absorption spectroscopy has been widely used in non-intrusive chemical analysis. Dual-comb spectroscopy is emerging as an effective tool for the measurement of absorption spectroscopy with both high resolution and wide bandwidth. Herein, we proposed a simple measurement of the absorption spectrum based on a polarization-multiplexed dual-comb laser. The free-running dual combs generated from a single cavity were highly coherent. In addition, the two combs possess overlapped spectra. Therefore, the dual-comb laser was utilized to perform dual-comb spectroscopy directly without a servo-locking system. The signal-to-noise ratio of interferograms in the time domain was effectively improved by the coherent average. The linear relationship between the signal-to-noise ratio and the square root of average times indicated the dual-comb laser was highly coherent. Taking advantage of the stable dual-comb laser, the extracted weak absorption features of hydrogen cyanide within the wavelength range of 1560 to 1566 nm were in line with the HITRAN database. To the best of our knowledge, it is the first time to realize the measurement of absorption spectrum at 1.5-µm with dual combs under such low repetition rates. Such kind of dual-comb laser provides an effective approach for the realization of low-cost and high-resolution absorption spectroscopy. The simple and high-resolution dual-comb spectrometer could be further applied in quantitative measurements based on absorption spectroscopy, such as measurements of temperature and concentration.