Sensitive multiplex spectroscopy in the molecular fingerprint 2.4 $\mu$m region with a Cr^{2+}:ZnSe femtosecond laser

TL;DR

This paper demonstrates a novel ultrashort-pulse Cr^{2+}:ZnSe laser as a broadband source for high-resolution, sensitive molecular spectroscopy in the 2.4 μm region, achieving rapid, high signal-to-noise measurements of gases like acetylene and ammonia.

Contribution

It introduces a femtosecond Cr^{2+}:ZnSe laser for fast, high-resolution molecular spectroscopy with significantly improved speed and sensitivity over traditional sources.

Findings

Achieved a 3800 signal-to-noise ratio in 13 seconds.

Demonstrated detection of HF at 0.2 ppbv level.

Showed laser-based spectroscopy is much faster than classical tungsten lamp methods.

Abstract

An ultrashort-pulse Cr^{2+}:ZnSe laser is a novel broadband source for sensitive high resolution molecular spectroscopy. A 130-fs pulse allows covering of up to 380 cm^-1 spectral domain around 2.4 $\mu$m which is analyzed simultaneously with a 0.12 cm^-1 (3.6 GHz) resolution by a Fourier-transform spectrometer. Recorded in 13 s, from 70-cm length absorption around 4150 cm^-1, acetylene and ammonia spectra exhibit a 3800 signal-to-noise ratio and a 2.4*10^-7 cm^-1*Hz^-1/2 noise equivalent absorption coefficient at one second averaging per spectral element, suggesting a 0.2 ppbv detection level for HF molecule. With the widely practiced classical tungsten lamp source instead of the laser, identical spectra would have taken more than one hour.