Wavelength modulation diode laser absorption signals from Doppler broadened absorption profiles

Abstract

It has previously been shown that the nth harmonic output from a wavelength modulation absorption spectrometry (WMS) instrumentation can be expressed in terms of various Fourier coefficients (primarily the nth) of the wavelength modulated lineshape function for the transition of the species under investigation. Explicit expressions for an arbitrary Fourier coefficient of a wavelength modulated Lorentzian lineshape function have previously been derived and used for predicting WMS signals from homogeneously (collisionally) broadened transitions. This work derives explicit expressions for an arbitrary Fourier coefficient of a wavelength modulated Gaussian shaped absorption profile, which thus makes possible the description of WMS signals also from inhomogeneously (Doppler) broadened absorption profiles.