Mid-infrared spectroscopy offers supreme sensitivity for the detection of trace gases, solids and liquids based on tell-tale vibrational bands specific to this spectral region. Here, we present a new platform for mid-infrared dual-comb Fourier-transform spectroscopy based on a pair of ultra-broadband subharmonic optical parametric oscillators pumped by two phase-locked thulium-fibre combs. Our system provides fast (7 ms for a single interferogram), moving-parts-free, simultaneous acquisition of 350,000 spectral data points, spaced by a 115 MHz intermodal interval over the 3.1–5.5 µm spectral range. Parallel detection of 22 trace molecular species in a gas mixture, including isotopologues containing isotopes such as ¹³C, ¹⁸O, ¹⁷O, ¹⁵N, ³⁴S, ³³S and deuterium, with part-per-billion sensitivity and sub-Doppler resolution is demonstrated. The technique also features absolute optical frequency referencing to an atomic clock, a high degree of mutual coherence between the two mid-infrared combs with a relative comb-tooth linewidth of 25 mHz, coherent averaging and feasibility for kilohertz-scale spectral resolution.

中红外光谱仪根据特定于该光谱区域的振动带，为检测痕量气体，固体和液体提供了最高的灵敏度。在这里，我们介绍了一个基于一对由两个锁相th光纤梳泵浦的超宽带次谐波光学参量振荡器的中红外双梳傅里叶变换光谱的新平台。我们的系统提供了快速的信号（单个干涉图为7 ms），无移动部件，同时采集了350,000个光谱数据点，在3.1–5.5 µm光谱范围内以115 MHz联运模式间隔隔开。平行检测混合气体中的22种痕量分子种类，包括含有¹³ C，¹⁸ O，¹⁷ O，¹⁵等同位素的同位素N，³⁴ S，³³ S和氘具有十亿分之一的灵敏度和亚多普勒分辨率。该技术还具有参考原子钟的绝对光频率，两个中红外梳之间的高度相干性（相对梳齿线宽为25 mHz），相干平均以及千赫兹级光谱分辨率的可行性。