TEMPORAL AND SPECTRAL GAIN DYNAMICS IN AN ACTIVELY MODELOCKED SEMICONDUCTOR-LASER

We apply a new electrical pump, optical probe spectroscopic technique using a fs Ti : sapphire laser to study the temporal and spectral gain dynamics of a modelocked external cavity semiconductor laser. The tem poral behaviour of the gain and the spectrum of the differential gain are directly obtained. The spectrum of the differential refractive ind ex is determined via a Kramers-Kronig transformation enabling us to de termine the wavelength dependence of the alpha parameter. From the dis cussion of these results, strategies, limits and solutions are propose d to improve the quality of modelocking of diode lasers consequently r esulting in pulse shortening. The proposals are experimentally verifie d for wavelength-detuned operation and for synchronous pumping with ul trashort optical pulses instead of electrical modulation.