Due to its fast and high resolution characteristics, dual-comb spectroscopy has attracted an increasing amount of interest since its first demonstration. In the terahertz frequency range where abundant absorption lines (finger prints) of molecules are located, multiheterodyne spectroscopy that employs the dual-comb technique shows an advantage in real-time spectral detection over the traditional Fourier transform infrared or time domain spectroscopies. Here, we demonstrate compact terahertz dual-comb spectroscopy based on quantum cascade lasers (QCLs). In our experiment, two free-running QCLs generate approximately 120 GHz wide combs centered at 4.2 THz, with slightly different repetition frequencies. We observe that $\sim$490 nW terahertz power coupling of one laser into the other suffices for laser-self-detecting the dual-comb spectrum that is registered by a microwave spectrum analyzer. Furthermore, we demonstrate practical terahertz transmission dual-comb spectroscopy with our device, by implementing a short air path at room temperature. Spectra are shown of semiconductor samples and of moist air, the latter allowing rapid monitoring of the relative humidity. Our devices should be readily extendable to perform imaging, microscopy and near-field microscopy in the terahertz regime.

中文翻译：

---

朝着采用自检测方案的紧凑型实时太赫兹双室光谱学迈进

自其首次演示以来，由于其快速和高分辨率的特性，双梳子光谱法引起了越来越多的关注。在太赫兹频率范围内，存在大量的分子吸收线（指纹），与传统的傅立叶变换红外或时域光谱相比，采用双梳技术的多外差光谱在实时光谱检测中显示出优势。在这里，我们演示了基于量子级联激光器（QCL）的紧凑型太赫兹双梳状光谱。在我们的实验中，两个自由运行的QCL产生大约120 GHz宽的梳，中心频率为4.2 THz，重复频率略有不同。我们观察到，一台激光器的$ \ sim $ 490 nW太赫兹功率耦合足以满足激光自检测由微波频谱分析仪记录的双梳状频谱的要求。此外，我们通过在室温下实现短风道，证明了实用的太赫兹透射双梳光谱技术。显示了半导体样品和潮湿空气的光谱，后者可以快速监控相对湿度。我们的设备应易于扩展，以在太赫兹范围内执行成像，显微镜和近场显微镜。后者可以快速监控相对湿度。我们的设备应易于扩展以在太赫兹范围内执行成像，显微镜和近场显微镜。后者可以快速监控相对湿度。我们的设备应易于扩展，以在太赫兹范围内执行成像，显微镜和近场显微镜。