Open AccessSingle-tone mid-infrared frequency modulation spectroscopy for sensitive detection of transient species
Author(s) -
Michael Stuhr,
Nancy Faßheber,
Gernot Friedrichs
Publication year - 2019
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.27.026499
Subject(s) - spectrometer , materials science , optics , excimer laser , laser , spectroscopy , infrared , frequency modulation , detector , detection limit , modulation (music) , absorption spectroscopy , infrared spectroscopy , ultrafast laser spectroscopy , analytical chemistry (journal) , chemistry , physics , bandwidth (computing) , computer network , chromatography , quantum mechanics , computer science , acoustics , organic chemistry
A single-tone mid-infrared frequency modulation (MIR-FM) spectrometer consisting of a cw-OPO-based laser system, a 500 MHz LiTaO 3 electro-optical modulator (EOM), and a high-bandwidth GaAs mid-infrared detector has been developed. In order to assess the instrument's sensitivity and time resolution, FM spectra of selected CH 4 transitions around 3070 cm -1 were measured and the reaction Cl + CH 4 following the 193 nm excimer laser photolysis of oxalyl chloride was investigated by recording concentration-time profiles of HCl at 2925.90 cm -1 in a low-pressure slow-flow reactor. Furthermore, OH radicals were generated by UV photolysis of H 2 O 2 and its transients were recorded at 3447.27 cm -1 . The minimal detectable absorption of the spectrometer was determined to be A min =4⋅10 -4 ( Δ f BW =1 MHz, ν ~=3447 cm -1 ) by using the Allan approach. Mainly due to thermal noise contributions of the easy-to-saturate photodetector, the detection limit is about a factor of 4 above the shot-noise limit. To the best of our knowledge, this work reports the first implementation of a single-tone MIR-FM spectrometer based on an external EOM modulation scheme and its use for the detection of transient molecular species.