High-Resolution Spectroscopy in the 11.6-15 {\mu}m Range by a Quasi-cw Difference-Frequency-Generation Laser Source

TL;DR

This paper introduces a widely tunable, high-resolution mid-infrared laser source based on difference-frequency generation, enabling detailed molecular spectroscopy and fingerprinting in the 11.6-15 μm range.

Contribution

It presents a novel DFG laser source with broad tunability and narrow linewidth, suitable for high-resolution molecular spectroscopy in the mid-infrared.

Findings

Resolved absorption features of multiple species in the mid-infrared.

Successfully measured the broadband spectrum of ethylene (C2H4).

Quantified self-broadening coefficients of spectral lines.

Abstract

We report an approach for high-resolution spectroscopy using a widely tunable laser emitting in the molecular fingerprint region. The laser is based on difference-frequency generation (DFG) in a nonlinear orientation-patterned GaAs crystal. The signal laser, a CO2 gas laser, is operated in a kHz-pulsed mode while the pump laser, an external-cavity quantum cascade laser, is finely mode-hop-free tuned. The idler radiation covers a spectral range of 11.6 - 15 {\mu}m with a laser linewidth of 2.3 MHz. We showcase the versatility and the potential for molecular fingerprinting of the developed DFG laser source by resolving the absorption features of a mixture of several species in the long-wavelength mid-infrared. Furthermore, exploiting the wide tunability and resolution of the spectrometer, we resolve the broadband absorption spectrum of ethylene (C2H4) over 13 - 14.2 {\mu}m and quantify the self-broadening coefficients of some selected spectral lines.