Terahertz Dual-Comb Spectroscopy: A Comparison between Time- and Frequency-Domain Operation Modes

Abstract In terahertz dual-comb spectroscopies (THz-DCSs), electrical time delay lines are utilized to replace the mechanical ones widely used in traditional terahertz time-domain spectroscopic systems (THz-TDSs). Due to the usage of electrical delay line, the sampling time is effectively prolonged and the consecutive terahertz pulses can be sampled continuously, which leads to the improvement of frequency resolution and makes it possible for THz-DCSs work in dual (frequency- and time-domain, FD and TD) operation modes. Here, a THz-DCS is established by using two repetition-frequency-locked femtosecond (fs) lasers with a slight repetition frequency difference. A spectrum analyzer is used to directly record the terahertz spectral data. Alternatively, the terahertz transient pulses are sampled and recorded, and the terahertz spectra are obtained by Fourier transforming the TD data. The experimental results show that the terahertz spectra acquired in FD and TD are in good agreement with each other. For the dual-mode THz-DCS, the wideband terahertz spectral information and the specified narrowband spectral information with high frequency resolution can be simultaneously acquired, which is helpful for searching sharp-peaked fingerprint spectral features in a broad terahertz frequency range.