Determination of the relaxation constants of a nonlinearly absorbing gas using a frequency-modulated laser

A method is proposed, new to nonlinear intracavity laser spectroscopy, of determining the relaxation constants of the level populations and the polarization of an absorbing gas from spectral features of the frequency modulation of oscillations of a single-mode laser containing a nonlinearly absorbing gas when the optical length of the laser is modulated harmonically. This method was used in experiments on methane at the 3.39 μ wavelength.