Minimum harmonic detection order for Rayleigh resolution in modulation spectroscopy

Karan D. Mohan; Mohammad A. Khan; Amin N. Dharamsi

doi:10.1117/12.679522

1 September 2006 Minimum harmonic detection order for Rayleigh resolution in modulation spectroscopy

Karan D. Mohan, Mohammad A. Khan, Amin N. Dharamsi

Proceedings Volume 6299, Remote Sensing of Aerosol and Chemical Gases, Model Simulation/Assimilation, and Applications to Air Quality; 62990P (2006) https://doi.org/10.1117/12.679522
Event: SPIE Optics + Photonics, 2006, San Diego, California, United States

Abstract

Wavelength Modulation Spectroscopy (WMS) utilizes low frequency modulation of the probe, followed by synchronous detection at the modulation frequency or at one of the harmonics. WMS provides a particularly useful tool for resolving highly disparate overlapping lines, because the high-order derivative-like structure of higher harmonics results in an enhancement of features, not possible with conventional ("direct") absorption spectroscopy. An important question, not yet systematically addressed in the literature is, "Given that in any measurement seeking to resolve overlapping spectra there is always a minimum harmonic detection order, how does one determine this order?" To address this issue, a Rayleigh-like criterion is defined and used to determine when two lines are barely resolved. Shannon's information theoretical principles are then used to calculate the information obtained when overlapping spectra are barely resolved at a particular harmonic. The results obtained allow one to predict the minimal harmonic detection order that should be used to resolve overlapping lines.

Citation Download Citation

Karan D. Mohan, Mohammad A. Khan, and Amin N. Dharamsi "Minimum harmonic detection order for Rayleigh resolution in modulation spectroscopy", Proc. SPIE 6299, Remote Sensing of Aerosol and Chemical Gases, Model Simulation/Assimilation, and Applications to Air Quality, 62990P (1 September 2006); https://doi.org/10.1117/12.679522

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