A two-laser beam technique for improving the sensitivity of low frequency open path tunable diode laser absorption spectrometer (OP-TDLAS) measurements

Israa L. Mohammad; Gary T. Anderson; Youhua Chen

doi:10.1117/12.2033564

19 September 2013 A two-laser beam technique for improving the sensitivity of low frequency open path tunable diode laser absorption spectrometer (OP-TDLAS) measurements

Israa L. Mohammad, Gary T. Anderson, Youhua Chen

Author Affiliations +

Proceedings Volume 8867, Infrared Remote Sensing and Instrumentation XXI; 88670E (2013) https://doi.org/10.1117/12.2033564
Event: SPIE Optical Engineering + Applications, 2013, San Diego, California, United States

Abstract

Open path tunable diode-laser absorption spectroscopy (OP-TDLAS) is a promising technique to detect low concentrations of possible biogenic gases on Mars. This technique finds the concentration of a gas by measuring the amount of laser light absorbed by gaseous molecules at a specific wavelength. One of the major factors limiting sensitivity in the TDLAS systems operating at low modulation frequencies is 1/f noise. 1/f noise is minimized in many spectroscopy systems by the use of high frequency modulation techniques. However, these techniques require complex instruments that include reference cells and other devices for calibration, making them relatively large and bulky. We are developing a spectroscopy system for space applications that requires small, low mass and low power instrumentation, making the high frequency techniques unsuitable. This paper explores a new technique using two-laser beam to reduce the affect of 1/f noise and increase the signal strength for measurements made at lower frequencies. The two lasers are excited at slightly different frequencies. An algorithm is used to estimate the noise in the second harmonic from the combined spectra of both lasers. This noise is subtracted from the signal to give a more accurate measurement of gas concentration. The error in estimation of 1/f noise is negligible as it corresponds to noise level made at much higher frequencies. Simulation results using ammonia gas and two lasers operating at 500 and 510 Hz respectively shows that this technique is able to decrease the error in estimation of gas concentration to 1/6 its normal value.

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Israa L. Mohammad, Gary T. Anderson, and Youhua Chen "A two-laser beam technique for improving the sensitivity of low frequency open path tunable diode laser absorption spectrometer (OP-TDLAS) measurements", Proc. SPIE 8867, Infrared Remote Sensing and Instrumentation XXI, 88670E (19 September 2013); https://doi.org/10.1117/12.2033564

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KEYWORDS

Interference (communication)

Signal to noise ratio

Error analysis

Semiconductor lasers

Modulation

Optical simulations

Absorption

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