Bending modes metrology in the 14-15 $\mu$m region

TL;DR

This paper introduces a new tunable MIR laser source enabling the first precise measurement of bending vibrational modes in the 14-15 μm range, advancing molecular spectroscopy and astrophysical research.

Contribution

A novel MIR laser source with broad tunability and high precision, facilitating bending mode metrology in a previously unexplored spectral region.

Findings

Achieved calibration of CO₂-based frequency benchmarks with 30 kHz uncertainty

Enabled accurate study of benzene's ν₁₁ vibrational band

Paved the way for LW-MIR metrology and astrophysical applications

Abstract

Frequency combs have triggered an impressive evolution of optical metrology across diverse regions of the electromagnetic spectrum, from the ultraviolet to the terahertz frequencies. An unexplored territory, however, remains in the region of vibrational bending modes, mostly due to the lack of single-mode lasers in the long-wavelength (LW) part of the mid-infrared (MIR) spectrum. We fill this gap through a purely MIR-based nonlinear laser source with tunability from 12.1 to 14.8 $\mu$m, optical power up to 110 $\mu$W, MHz-level linewidth and comb calibration. This enables the first example of bending modes metrology in this region, with the assessment of several CO$_2$-based frequency benchmarks with uncertainties down to 30 kHz, and the accurate study of the $\nu_{11}$ band of benzene, which is a significant testbed for the resolution of the spectrometer. These achievements pave the way for LW-MIR metrology, rotationally-resolved studies and astronomic observations of large molecules, such as aromatic hydrocarbons.