Analysis of modal chirp in Q-switched semiconductor lasers

Time-resolved spectroscopic measurements of Q-switched laser pulses are presented in the picosecond time scale for different AlGaAs lasers operating either in single-mode or multimode regime. Single-mode operation is achieved by injection of a weak CW laser beam in the cavity. Measurements are performed for pulse energies up to 15 pJ, which is about one order of magnitude higher than in previous works. It is shown that the modal chirp amplitude only depends on the total pulse energy whether the laser is single-mode or multimode. An almost linear increase of the modal chirp with pulse energy is found. A quantitative estimation of the alpha factor shows that values higher than 30 can be attained in Q-switched lasers.