Continuously tunable frequency-doubled CO2-laser-based photoacoustic spectrometer for trace gas detection

Albert Romann; Markus W. Sigrist

doi:10.1117/12.469856

10 June 2002 Continuously tunable frequency-doubled CO₂-laser-based photoacoustic spectrometer for trace gas detection

Albert Romann, Markus W. Sigrist

Proceedings Volume 4618, Biomedical Optoacoustics III; (2002) https://doi.org/10.1117/12.469856
Event: International Symposium on Biomedical Optics, 2002, San Jose, CA, United States

Abstract

We present a pulsed photoacoustic (PA) spectrometer based on a frequency doubled, continuously tunable high pressure CO₂ laser. A quasi-phasematched diffusion-bonded GaAs crystal is implemented for second harmonic generation (SHG) and has advantages over well-known non-linear infrared (IR) materials such as AgGaSe₂ and ZnGeP₂, like high-average power capabilities, and high damage threshold. GaAs has a large non-linear coefficient (d₁₄ = d₃₆ = 150 pm/V), is transparent in the range 1 - 16 m, features low absorption and high thermal conductivity, but it is not birefringent. The periodically poled crystal is anti-reflection-coated (AR) for the 10 m and 5 m range, and consists of 53 GaAs plates of ~106 m thickness for first-order quasi-phase-matching. With 80 mJ pump energy we achieved up to 1 mJ SHG pulse energy. A non-resonant PA gas cell equipped with an 80-microphone-array is employed sealed-off and in flow mode. We use the fundamental as well as the SHG radiation for our spectroscopic measurements. To our best knowledge, we present the first PA spectra measured with such a system in the 5 m range, e. g., on NO buffered in N₂ at atmospheric pressure and room temperature. The performance of this novel PA spectrometer is illustrated by various examples of biological interest.

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Albert Romann and Markus W. Sigrist "Continuously tunable frequency-doubled CO₂-laser-based photoacoustic spectrometer for trace gas detection", Proc. SPIE 4618, Biomedical Optoacoustics III, (10 June 2002); https://doi.org/10.1117/12.469856

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KEYWORDS

Gas lasers

Carbon monoxide

Second-harmonic generation

Spectroscopy

Photoacoustic spectroscopy

Gallium arsenide

Crystals

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