Video-rate broadband longwave IR dual-comb spectroscopy with 240,000 comb-mode resolved data points

TL;DR

This paper demonstrates video-rate broadband longwave IR dual-comb spectroscopy with high spectral resolution and signal-to-noise ratio, enabling real-time molecular detection using highly coherent LWIR combs generated via intra-pulse difference frequency generation.

Contribution

It introduces a novel dual-comb spectroscopy system operating at video rates with high resolution and SNR, utilizing intra-pulse difference frequency generation in ZGP crystals with sub-three-cycle pulses.

Findings

Achieved real-time molecular spectra acquisition at 0.1-12 s per spectrum.

Generated highly coherent broadband LWIR combs with 300 mW power per channel.

Resolved approximately 240,000 comb modes with high SNR.

Abstract

We report molecular detection using dual frequency-comb spectroscopy with highly coherent broadband (6.6-11.4 {\m}m) long-wavelength infrared (LWIR) combs. The combs were produced via intra-pulse difference frequency generation (IDFG) in ZGP crystals using sub-three-cycle (20 fs) driving pulses from mode-locked Cr:ZnS lasers at the central wavelength of 2.4 {\m}m). Real-time and up to video rate (0.1-12 s per spectrum) acquisition of molecular spectra with some 240,000 comb-mode-resolved data points spaced by 80 MHz and referenced to a Rb clock with a signal-to-noise ratio (SNR) >300 has been demonstrated. The key to achieving such a high rate of massive spectral data acquisition is a low phase and intensity noise of the LWIR combs and excellent mutual coherence. The high SNR was also facilitated by the high (7.5%) IDFG conversion efficiency resulting in an average LWIR comb power of 300 mW per channel.