Bandwidth-limited picosecond pulses from an injection GaAlAs DH laser with an external dispersive cavity

Mode locking of semiconductor lasers with external dispersive cavities is investigated both experimentally and theoretically. The external cavity consists of a microscope objective and a diffraction grating. Bandwidth-limited tunable picosecond pulses (FWHM about 3 ps and
\Delta\tau . \Delta\nu = 0.30
) are obtained with such a configuraton. The pulse duration is measured by a second-harmonic generation (SHG) correlation method and an ultrafast streak camera. Theoretical investigations of mode locking based on the time-domain approach and pulse propagation through the elements of the ring laser cavity are carried out. The laser medium is considered to be divided into two parts-the amplifying and absorbing regions. The steady state pulse parameters (duration, energy, and asymmetry) are derived from the computer simulation and are compared with the experiment. The effects of gain and absorber saturation are included in the treatment.