Gigahertz Single-cavity Dual-comb Laser for Rapid Time-domain Spectroscopy: from Few Terahertz to Optical Frequencies

TL;DR

This paper introduces a compact, single-cavity dual-comb laser operating at gigahertz rates, enabling rapid, high-resolution time-domain spectroscopy across a broad frequency range, with applications in near-infrared and THz spectroscopy.

Contribution

The work demonstrates a novel single-cavity dual-comb laser with high repetition rate differences and sub-100 fs pulses, enabling efficient THz generation and precise time sampling in a simplified setup.

Findings

Achieved dual-comb operation at >100 kHz difference with sub-100 fs pulses.

Demonstrated THz spectroscopy up to 3 THz with near-GHz spectral resolution.

Confirmed ultra-low timing jitter and high stability in free-running operation.

Abstract

Dual-comb generation from a single laser cavity provides a simple and high-performance solution to time sampling applications. We demonstrate a compact single-cavity dual-comb laser operating at gigahertz repetition rates and high repetition rate differences up to more than 100 kHz with sub-100 fs pulse duration. The single cavity approach leads to passive common noise suppression resulting in ultra-low relative timing jitter and fully resolvable comb lines in free-running operation. We showcase the laser performance with two application demonstrations: (a) time-domain spectroscopy of acetylene in the near-infrared via computational comb line tracking and (b) free-space THz time domain spectroscopy and thickness-measurements via adaptive sampling. For (b) we use efficient state-of the art iron-doped InGaAs photoconductive antennas to generate and detect the THz light. Here we operate these devices with an efficient Yb-based gigahertz repetition rate laser for the first time. One optical comb generates the THz light, while the other probes it via equivalent time sampling. We obtain signal strengths comparable to reference measurements with MHz repetition rate Er-based laser systems while achieving close to 1 GHz spectral resolution (defined by the comb line spacing) and generating THz frequencies up to 3 THz. By carrying out a careful investigation of the noise properties of the laser we confirm that the free-running gigahertz dual-comb oscillator provides a rapid yet highly precise optical delay sweep from a simple setup. Therefore, our approach will be beneficial for high-update rate time sampling and time-domain spectroscopy applications.