Triggerless data acquisition in asynchronous optical-sampling terahertz time-domain spectroscopy based on dual-comb system

TL;DR

This paper presents a triggerless, high-precision terahertz spectroscopy system using dual-comb optical sources, enabling long-duration data acquisition without signal degradation and accurate spectral measurements.

Contribution

It introduces a triggerless ASOPS THz-TDS system with phase-locked frequency combs, eliminating the need for optical delay lines and trigger signals, and demonstrating high stability and accuracy.

Findings

Achieved triggerless data acquisition over 48 minutes

Demonstrated high frequency stability of ~8.0×10^{-17} after 730 seconds

Accurately measured water vapor absorption line consistent with HITRAN database

Abstract

By using two mutually phase-locked optical frequency combs with slightly different repetition rates, we demonstrate asynchronous optical-sampling terahertz time-domain spectroscopy (ASOPS THz-TDS) without using any trigger signals or optical delay lines. Due to a tight stabilization of the repetition frequencies, it was possible to accumulate the data over 48 minutes in a triggerless manner without signal degradation. The fractional frequency stability of the measured terahertz signal is evaluated to be $\sim$8.0$\times$10$^{- 17}$ after 730 s. The frequency accuracy of the obtained terahertz spectrum is ensured by phase-locking the two frequency combs to a frequency standard. To clarify the performance of our system, we characterized the absorption line of water vapor around 0.557 THz. The good agreement of the measured center frequency and linewidth with the values predicted from the HITRAN database verifies the suitability of our ASOPS THz-TDS system for precise measurements.