Resonant Self-Focusing and Non-Stationary Coherent Transients Manifestations in Frequency-Modulated Laser Beams Propagation

Periodical modulation of frequency, typical for spectroscopic purposes, is numerically modelled in transversely limited, propagating through a saturable two-level absorber. At modulation periods comparable with the atomic relaxation times the time and frequency dependence of the output intensity exhibits the manifestations of delayed medium response, including time-dependent lens and aperture effects that may be of importance in spectroscopy