Wavelength modulation laser spectroscopy of N$_2$O at 17 $\mu$m

TL;DR

This study uses wavelength modulation laser spectroscopy with a quantum cascade laser to precisely measure N₂O spectral lines at 17 μm, providing data useful for spectrometer calibration and developing frequency references.

Contribution

It introduces a detailed lineshape model for wavelength modulation spectroscopy and provides new high-precision measurements of N₂O ro-vibrational transitions in the 17 μm region.

Findings

Measured N₂O transition frequencies with <5 MHz uncertainty.

Developed a comprehensive lineshape model considering multiple broadening effects.

Provided spectroscopic parameters for N₂O vibrational states.

Abstract

Using a mid-infrared quantum cascade laser and wavelength modulation absorption spectroscopy, we measure the frequencies of ro-vibrational transitions of N$_2$O in the 17 $\mu$m region with uncertainties below 5 MHz. These lines, corresponding to the bending mode of the molecule, can be used for calibration of spectrometers in this spectral region. We present a model for the lineshapes of absorption features in wavelength modulation spectroscopy that takes into account Doppler broadening, collisional broadening, saturation of the absorption, and lineshape distortion due to frequency and intensity modulation. Combining our data with previous measurements, we provide a set of spectroscopic parameters for several vibrational states of N$_2$O. The lines measured here fall in the same spectral region as a mid-infrared frequency reference that we are currently developing using trapped, ultracold molecules. With such a frequency reference, the spectroscopic methods demonstrated here have the potential to improve frequency calibration in this part of the spectrum.