Two-wavelength quantum cascade lasers with heterogeneous cascades

Quantum cascade (QC) lasers with a dual-wavelength interdigitated cascade are presented. Their active core consists of a stack of active regions and injectors emitting at 8.0 mum interleaved with a second stack emitting at 9.5 mum. Laser action at two substantially different wavelengths is observed, demonstrating the viability of the "interdigitated cascade" approach for multi-wavelength laser emission in the mid-infrared. This laser was also used to investigate the influence of the injector-doping on the device perfomance. Two QC lasers with different injector-doping levels were measured, in particular one only doped in the injectors bridging the 8.0 mum active region to the 9.5 mum active region and the remaining injectors undoped. A substantial reduction in threshold was observed for the laser wavelength with the undoped injector, confirming the significance of impurity scattering for the laser threshold in QC-lasers. Dual single-mode and tunable emission at two substantially different wavelength could be demonstrated with a QC laser emitting at 5.0 mum and 7.5 mum simultaneously. These lasers may be of interest for trace gas sensing, as the second wavelength could be used as in-built reference channel.