Novel pathlength saturation effects in modulation spectroscopic techniques

M. A. Khan; K. D. Mohan; A. N. Dharamsi

doi:10.1117/12.685642

25 October 2006 Novel pathlength saturation effects in modulation spectroscopic techniques

M. A. Khan, K. D. Mohan, A. N. Dharamsi

Proceedings Volume 6378, Chemical and Biological Sensors for Industrial and Environmental Monitoring II; 63780C (2006) https://doi.org/10.1117/12.685642
Event: Optics East 2006, 2006, Boston, Massachusetts, United States

Abstract

Wavelength Modulation Spectroscopy (WMS) has been extensively used as a tool for sensitive detection through precise measurements of the absorption lineshape function of gaseous species. In this paper pathlength saturation in wavelength modulation spectroscopy is studied. New effects are found when one takes advantage of demodulation at higher harmonics of the modulation frequency. We show here that modulation spectroscopy is a much more sensitive probe of these effects. In particular, when synchronous detection is performed at higher harmonics of the modulation frequency, even very small pathlength saturation effects become clearly visible. The method discussed allows one to probe lineshape profiles by observing how the signal profile varies with absorption pathlength. In particular, the signal around line center displays effects of saturation that are characteristic of the lineshape. This method is powerful because, ultimately, all the information about any measurement is contained in the lineshape profile. Since different lineshape profiles exhibit different saturation behavior, higher harmonic detection provides a new method to perform sensitive detection. We have shown effects of saturation on the central lobes of harmonic signals. We also show that there are definite relationships between the variation of the individual side lobes as well as their relative magnitudes that yield further information about the lineshape function.

Citation Download Citation

M. A. Khan, K. D. Mohan, and A. N. Dharamsi "Novel pathlength saturation effects in modulation spectroscopic techniques", Proc. SPIE 6378, Chemical and Biological Sensors for Industrial and Environmental Monitoring II, 63780C (25 October 2006); https://doi.org/10.1117/12.685642

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