Absolute spectroscopy near 7.8 {\mu}m with a comb-locked extended-cavity quantum-cascade-laser

TL;DR

This paper demonstrates the first frequency-locking of an extended-cavity quantum-cascade-laser to a near-infrared frequency comb, enabling precise absolute spectroscopy near 7.8 μm with high accuracy and potential for extension to longer wavelengths.

Contribution

It introduces a novel locking scheme for EC-QCLs to frequency combs, allowing accurate line center measurements in the mid-infrared region outside current tunable laser capabilities.

Findings

Achieved ~60 kHz accuracy in N2O line measurements.

Demonstrated single mode operation over 100 cm^{-1}.

Potential to extend technique up to 12 μm.

Abstract

We report the first experimental demonstration of frequency-locking of an extended-cavity quantum-cascade-laser (EC-QCL) to a near-infrared frequency comb. The locking scheme is applied to carry out absolute spectroscopy of N2O lines near 7.87 {\mu}m with an accuracy of ~60 kHz. Thanks to a single mode operation over more than 100 cm^{-1}, the comb-locked EC-QCL shows great potential for the accurate retrieval of line center frequencies in a spectral region that is currently outside the reach of broadly tunable cw sources, either based on difference frequency generation or optical parametric oscillation. The approach described here can be straightforwardly extended up to 12 {\mu}m, which is the current wavelength limit for commercial cw EC-QCLs.