High-Resolution Quantum Cascade Laser Dual-Comb Spectroscopy in the Mid-Infrared with Absolute Frequency Referencing

TL;DR

This paper presents a novel frequency calibration scheme enabling high-resolution dual-comb spectroscopy with quantum cascade lasers, achieving 600 kHz accuracy in rapid measurements, advancing MIR molecular fingerprinting.

Contribution

The authors developed a new calibration method for QCL combs that allows fast, high-precision spectroscopy suitable for complex molecular analysis in the mid-infrared.

Findings

Achieved 600 kHz spectral accuracy in 54-ms measurements

Demonstrated dual-comb spectroscopy over 40 cm$^{-1}$ range

Calibration scheme applicable to micro-combs and other setups

Abstract

Quantum cascade laser (QCL) frequency combs have revolutionized mid-infrared (MIR) spectroscopy by their high brightness and fast temporal resolution, and are a promising technology for fully-integrated and cost-effective sensors. As for other integrated comb sources such as micro-combs and interband cascade laser, QCLs have a comb spacing of several GHz, which is adequate for measurements of wide absorbing structures, typically found in liquid or solid samples. However, high-resolution gas-phase spectra require spectral interleaving and frequency calibration. We developed a frequency calibration scheme for fast interleaved measurements with combs featuring multi-GHz spacing. We then demonstrate dual-comb spectroscopy with 600 kHz accuracy in single-shot 54-ms measurements over 40 cm$^{-1}$ using two QCLs at 7.8 $\mathrm{\mu}$m. This work is an important contribution towards fast fingerprinting of complex molecular mixtures in the MIR. Moreover, the calibration scheme could be used with micro-combs for spectroscopy and ranging, both in comb-swept and comb-calibrated setups.