Characteristic features of field broadening in intracavity frequency-modulation spectroscopy

An analysis is made of the characteristic features of the field-induced broadening in intracavity frequency-modulation spectroscopy. Simple but effective methods for eliminating field broadening of nonlinear resonances are proposed. It is shown that in the case of frequency-modulation resonances of the dispersion and absorption, which set the detuning from the center of the absorption line to a value equal to the modulation frequency, and also in the case of dispersion resonances, which set the detuning at zero, it is possible to avoid the field-induced broadening by a suitable selection of a specific frequency modulation index.