Spectral tuning and mode competition of quantum cascade lasers studied by time-resolved Fourier transform spectroscopy

We present a study of the spectral characteristics of Fabry-Perot quantum cascade lasers in pulsed mode operation applying a time resolution of 3 ns in combination with a high spectral resolution of 0.02 cm -1 . With this technique the laser spectra were investigated applying pulse lengths ranging between 100 ns and 20 μs and duty cycles between 0.01% and 10%. Depending on the current density and operation temperature, the spectra exhibit complex line patterns, which indicate mode competition caused by gain saturation effects.