Abstract
Dual-comb spectroscopy (DCS) is useful for gas spectroscopy due to high potential of optical frequency comb (OFC). However, fast Fourier transform (FFT) calculation of a huge amount of temporal data spends significantly longer time than the acquisition time of an interferogram. In this article, we demonstrate frequency-domain DCS by a combination of DCS with lock-in detection, namely LID-DCS. LID-DCS directly extracts an arbitrary OFC mode from a vast number of OFC modes without the need for FFT calculation. Usefulness of LID-DCS is demonstrated in rapid monitoring of transient signal change and spectroscopy of hydrogen cyanide gas.
Highlights
Recent advances in optical frequency comb (OFC) [1,2,3] enable us to benefit from a group of a vast number of phase-locked narrow-linewidth continuous-wave (CW) lights with a constant frequency spacing frep over a broad spectral range
The net measurement time was defined as an acquisition time of accumulated signal for lock-in detection (LID)-Dual-comb spectroscopy (DCS) and a sum of acquisition time of a single interferogram or consecutive interferograms and fast Fourier transform (FFT) calculation time for DCS
In LID-DCS, the net measurement time is determined by the LID time constant and the number of signal accumulation; in DCS, most of the net measurement time is occupied by the FFT calculation time rather than the acquisition time of interferogram
Summary
Recent advances in optical frequency comb (OFC) [1,2,3] enable us to benefit from a group of a vast number of phase-locked narrow-linewidth continuous-wave (CW) lights with a constant frequency spacing frep (typically, 50 to 100 MHz) over a broad spectral range. The inherent mode-locking nature and active laser control make it possible to use the OFC as an optical frequency ruler traceable to a microwave or radio-frequency (RF) frequency standard. To fully utilize both its narrow spectral linewidth and broadband spectral coverage for broadband spectroscopy, it is essential to acquire the mode-resolved OFC spectrum. Virtually-imaged-phased-array (VIPA) spectroscopy [6, 7, 8] is a promising method for rapid acquisition of mode-resolved OFC spectrum. VIPA spectroscopy is limited for OFCs with frep larger than a few GHz due to its spectral resolving power
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