Abstract-Towards Compact and Real-Time Terahertz Dual-Comb Spectroscopy Employing a Self-Detection Scheme

Hua Li, Ziping Li, Wenjian Wan, Kang Zhou, Xiaoyu Liao, Sijia Yang, Chenjie Wang, J. C. Cao, Heping Zeng

https://arxiv.org/abs/1904.03330

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 150 GHz wide combs centered at 4.2 THz, with slightly different repetition frequencies. We observe that ∼270 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.

Abstract-Combination of lock-in detection with dual-comb spectroscopy

Hidenori Koresawa, Kyuki Shibuya,  Takeo Minamikawa,  Akifumi Asahara,  Kaoru Minoshima,  Takeshi Yasui

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10925/109251A/Combination-of-lock-in-detection-with-dual-comb-spectroscopy/10.1117/12.2509619.short?SSO=1

Dual-comb spectroscopy (DCS) is a powerful tool for gas spectroscopy due to high resolution, high accuracy, broadband spectral coverage, and rapid data acquisition, based on optical frequency comb (OFC) traceable to a frequency standard. In DCS, after a temporal waveform of interferogram is acquired in time domain, the corresponding mode-resolved OFC spectrum is obtained by fast Fourier transform (FFT) calculation of the acquired interferogram. However, FFT calculation of huge-sized temporal data spends significantly longer time than the acquisition time of interferogram, making it difficult to response the transient signal change. In this article, we demonstrate frequency-domain DCS by a combination of DCS with lock-in detection (LID), namely LID-DCS. LID-DCS directly extracts an arbitrary OFC mode from a vast number of OFC modes without the need for FFT calculation by the synchronous detection at a LID reference frequency while maintaining high resolution and high accuracy. Usefulness of LID-DCS is demonstrated in rapid monitoring of transient signal change and spectroscopy of hydrogen cyanide gas by comparing with usual DCS.

© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Abstract-Scan-less hyperspectral dual-comb single-pixel-imaging in both amplitude and phase

Kyuki Shibuya, Takeo Minamikawa, Yasuhiro Mizutani, Hirotsugu Yamamoto, Kaoru Minoshima, Takeshi Yasui, and Tetsuo Iwata

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-18-21947

We have developed a hyperspectral imaging scheme that involves a combination of dual-comb spectroscopy and Hadamard-transform-based single-pixel imaging. The scheme enables us to obtain 12,000 hyperspectral images of amplitude and phase at a spatial resolution of 46 µm without mechanical scanning. The spectral resolution given by the data point interval in the frequency domain is 20 MHz and the comb mode interval is 100 MHz over a spectral range of 1.2 THz centered at 191.5 THz. As an initial demonstration of our scheme, we obtained spectroscopic images of a standard test chart through an etalon plate. The thickness of an absorptive chromium-coated layer on a float-glass substrate was determined to be 70 nm from the hyperspectral phase images in the near-infrared wavelength region.

© 2017 Optical Society of America

Abstract-Dual-comb spectroscopy

Ian Coddington, Nathan Newbury, and William Swann
https://www.osapublishing.org/optica/abstract.cfm?uri=optica-3-4-414

Dual-comb spectroscopy is an emerging new spectroscopic tool that exploits the frequency resolution, frequency accuracy, broad bandwidth, and brightness of frequency combs for ultrahigh-resolution, high-sensitivity broadband spectroscopy. By using two coherent frequency combs, dual-comb spectroscopy allows a sample’s spectral response to be measured on a comb tooth-by-tooth basis rapidly and without the size constraints or instrument response limitations of conventional spectrometers. This review describes dual-comb spectroscopy and summarizes the current state of the art. As frequency comb technology progresses, dual-comb spectroscopy will continue to mature and could surpass conventional broadband spectroscopy for a wide range of laboratory and field applications.

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