Self-stabilization of ultrashort pulses emitted by a neodymium phosphate glass laser

An investigation was made of the emission spectra of a neodymium phosphate glass laser during various stages of formation of ultrashort pulses. The kinetics of the spectrum of free lasing with passive mode locking was observed first. Considerable changes in the spectrum were observed for successive free-lasing spikes, which made it impossible to achieve self-stabilization of the ultrashort pulse duration. The spectrum of ultrashort pulses varied with the point of selection of a pulse in a train. The results were explained allowing for the simultaneous influence of burning of spectral holes in the population inversion and phase self-modulation on the operation of a laser with passive mode locking.