(Optical Society of America, 2009-12-01) Wang, Christine Y.; Kuznetsova, Lyuba; Gkotsas, VasileiosāMarios; Diehl, L; Kaertner, Franz X.; Belkin, Mikhail A.; Belyanin, Alexey; Li, Xiaofeng; Ham, Donhee; Schneider, Harald; Grant, Peter; Song, C. Y.; Haffouz, Soufien; Wasilewski, Zbigniew; Liu, H. C.; Capasso, Federico
In this study, we report the unequivocal demonstration of midinfrared mode-locked pulses from quantum cascade lasers. The train of short pulses was generated by actively modulating the current and hence the gain of an edge-emitting quantum cascade laser (QCL). Pulses with duration of about 3 ps at full-width-at-half-maxima and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modeled based on the Maxwell-Bloch equations in an open two-level system. Our model reproduces the overall shape of the measured autocorrelation traces and predicts that the short pulses are accompanied by substantial wings as a result of strong spatial hole burning. The range of parameters where short mode-locked pulses can be formed is found.
