Cavity-enhanced spectroscopic instruments impact a broad range of scientific fields because they are sensitive, self-contained, and can be packaged for use by nonspecialists. Infrared-laser-based cavity-enhanced instruments are typically limited to measuring a few small molecules because they rely on narrowly tunable lasers that each measure a molecular transition. Broadband dual-comb spectroscopy (DCS) is a spectroscopic technique capable of simultaneously probing molecular absorption on thousands of narrowly spaced wavelengths using a single high-speed photodetector. With coherent averaging, DCS can measure multiple species, including large molecules, with a high signal-to-noise ratio (SNR). Here, we lock a high-finesse optical cavity to a broadband mode-locked frequency comb with an approach that enables a high SNR, broadband cavity-enhanced DCS with coherent averaging. With a 7.5 cm optical cavity, we attain a $>12,000\times$ path-length-enhancement factor, 60 nm bandwidth near 1660 nm (3.5% fractional bandwidth), and $>27\mathrm{dB}$ SNR in 160 s. We measure the dense rovibrational spectrum of ethane in a background of overlapping ${\mathrm{H}}_2\mathrm{O}$, ${\mathrm{CH}}_4$, and ${\mathrm{CO}}_2$ absorption. By combining the broadband, high-resolution, and single-detector nature of DCS with a compact optical cavity, we enable future self-contained instruments that are able to simultaneously detect a variety of molecules in realistic ambient conditions.

中文翻译：

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宽带相干腔增强双梳谱

腔增强光谱仪器影响广泛的科学领域，因为它们灵敏，自成体系，并且可以包装供非专业人员使用。基于红外激光的腔增强仪器通常仅限于测量一些小分子，因为它们依赖于每个分子均能测量分子跃迁的窄可调激光器。宽带双梳光谱仪（DCS）是一种光谱技术，能够使用单个高速光电探测器同时探测数千个窄间距波长上的分子吸收。通过相干平均，DCS可以测量具有高信噪比（SNR）的多种物种，包括大分子。在这里，我们采用高信噪比的方法将高端光学腔锁定到宽带锁模频率梳，相干平均的宽带腔增强DCS。使用7.5厘米的光学腔，我们可以达到$>12，000\times$ 路径长度增强因子，1660 nm附近的60 nm带宽（3.5％的小数带宽）和 $>27\mathrm{D\; b}$SNR在160秒内。我们在重叠的背景下测量乙烷的致密旋转振动光谱${\mathrm{H}}_{\mathrm{2个}}\mathrm{Ø}$， ${\mathrm{CH}}_4$， 和 ${\mathrm{一氧化碳}}_{\mathrm{2个}}$吸收。通过将DCS的宽带，高分辨率和单检测器特性与紧凑的光学腔相结合，我们使未来的独立仪器能够在现实的环境条件下同时检测多种分子。