Field deployable TDLAS for long path atmospheric transmission

Christopher A. Rice; Glen P. Perram

doi:10.1117/12.972407

1 November 2012 Field deployable TDLAS for long path atmospheric transmission

Christopher A. Rice, Glen P. Perram

Proceedings Volume 8535, Optics in Atmospheric Propagation and Adaptive Systems XV; 853507 (2012) https://doi.org/10.1117/12.972407
Event: SPIE Remote Sensing, 2012, Edinburgh, United Kingdom

Abstract

A tunable diode laser absorption spectroscopy (TDLAS) device with narrow band (~300 kHz) diode laser fiber coupled to a pair of 12.5" Ritchey-Chrétien telescopes was used to study atmospheric propagation. The ruggedized system has been field deployed and tested for propagation distances of greater than 1 km. By scanning the diode laser across many free spectral ranges, many rotational absorption features are observed. Absolute laser frequency is monitored with a High Fineese wavemeter to an accuracy of 2 MHz. Phase sensitive detection is employed with absorbance of < 1% observable under field conditions. More than 50 rotational lines in the molecular oxygen A-band X-b (0,0) transition near 760 nm were observed. Temperatures were determined from the Boltzmann rotational distribution to within 1.3% (less than ±2 K). Oxygen concentration was obtained from the integrated spectral area of the absorption features to within 1.6% (less than ± 0.04 x 10¹⁸ molecules / cm³). Pressure was determined independently from the pressure broadened Voigt lineshapes to within 10%. A Fourier Transform Interferometer (FTIR) was also used to observe the absorption spectra at 1 cm^-1 resolution. The TDLAS approach achieves a minimum observable absorbance of 0.2%, whereas the FTIR instrument is almost 20 times less sensitive. Applications include atmospheric characterization for high energy laser propagation and validation of monocular passive raging. The cesium Diode Pumped Alkali Laser (DPAL) operates near 894 nm, in the vicinity of atmospheric water vapor absorption lines. Water vapor concentrations are accurately retrieved from the observed spectra using the HITRAN database.

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Christopher A. Rice and Glen P. Perram "Field deployable TDLAS for long path atmospheric transmission", Proc. SPIE 8535, Optics in Atmospheric Propagation and Adaptive Systems XV, 853507 (1 November 2012); https://doi.org/10.1117/12.972407

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KEYWORDS

Absorption

Atmospheric propagation

Semiconductor lasers

Absorbance

Cesium

Oxygen

Atmospheric modeling

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