Observation of Terahertz Frequency Comb and Application for Spectroscopy

Abstract

We observed the hyperfine-structured spectrum of a terahertz (THz) frequency comb with asynchronousoptical- sampling THz time-domain spectroscopy by extending the measured time window of the pulsed THz electric field by up to ten pulse periods. The observed THz comb mode, having a linewidth of 25 MHz and a frequency interval of 250 MHz, can be used as a precise and accurate frequency marker for broadband THz spectrum because it is traceable to a microwave frequency standard via laser control. We further demonstrated THz spectroscopy of sugar tablets and low-pressure water vapor based on THz comb, indicating that the proposed method enables high-accuracy, high-resolution, and broadband THz spectroscopy.