The achievable instrument sensitivity is a critical parameter for the continued development of terahertz (THz) applications. Techniques such as cavity-enhanced techniques and cavity ring-down spectroscopy have not yet been employed at THz frequency due to the difficulties to construct a high-finesse Fabry–Pérot cavity. Here, we describe such a THz resonator based on a low-loss oversized corrugated waveguide with highly reflective photonic mirrors obtaining a finesse above 3000 around 620 GHz. These components enable a Fabry–Pérot THz absorption spectrometer with an equivalent interaction length of 1 km giving access to line intensities as low as ${10}^{-27}{\mathrm{cm}}^{-1}/(\text{molecule}/{\mathrm{cm}}^2)$ with a S/N ratio of 3. In addition, the intracavity optical power has allowed the Lamb dip effect to be studied with a low-power emitter; an absolute frequency accuracy better than 5 kHz can be easily obtained providing an additional solution for rotational spectroscopy.

中文翻译：

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使用高级Fabry–Pérot腔的太赫兹气相光谱

可达到的仪器灵敏度是太赫兹（THz）应用持续发展的关键参数。由于难以构建高精细的法布里-珀罗腔，因此尚未在THz频率使用诸如腔增强技术和腔衰荡光谱学等技术。在这里，我们描述了一种基于THz谐振器，该谐振器基于具有高反射光子镜的低损耗超大型波纹状波导，在620 GHz频率下可获得3000以上的精细度。这些组件使法布里-珀罗特THz吸收光谱仪的等效相互作用长度为1 km，从而可以获得低至的谱线强度。${10}^{-27}{\mathrm{厘米}}^{-\mathrm{1个}}/（\text{分子}/{\mathrm{厘米}}^{\mathrm{2个}}）$信噪比为3。此外，腔内光功率允许使用低功率发射器研究羔羊倾角效应。可以轻松获得优于5 kHz的绝对频率精度，从而为旋转光谱学提供了另一种解决方案。