Femtosecond studies of spectral hole burning in semiconductor lasers

In order to investigate spectral hole burning in the gain region, we used a new heterodyne multiple wavelength pump-probe technique to study gain dynamics in strained-layer InGaAs/AlGaAs SQW diode lasers. Taking advantage of the spectral resolution provided by this technique, the spectral hole burning effects could be separated from other effects and directly identified. The strain induced heavy and light hole band splitting allowed us to choose experimental conditions where only a single transition contributed to the gain. This avoids the ambiguity of multiple spectral holes and simplifies the interpretation of the experimental data. Under high bias, a blue shift was observed. These studies are the first direct femtosecond measurements of the spectral dependence of ultrafast gain dynamics in diode lasers