Dual-wavelength homogeneous mid-infrared quantum cascade laser

We demonstrate a dual wavelength mid-infrared Quantum Cascade Laser (QCL) utilizing a single active region to emit at 5-μm and 9-μm. The novelty lies in the large energy difference between the two lasing energies, achieved through simultaneous injection into the top 2 levels of a 4-level cascade employing InGaAs/InAlAs heterostructures latticematched to InP. The gain and losses at both wavelengths were measured by two different methods, Hakki-Paoli and cutback method, and were compared with theoretical predictions. The results for the gain of the 9-μm laser from the two techniques are consistently lower than theoretical predictions. Moreover, the mid-infrared losses are larger than expected at both wavelengths. We are investigating these devices for their potential application of quantum coherence to achieve lasing without inversion. The intense fields generated by the 9-μm laser are expected to partially eliminate the resonant absorption on the transition of interest at an energy corresponding to the difference between the energies of the two lasers. Our results on the dual wavelength QCL provide insights in the detail charge transport and optical properties of this design concept and open up the possibility for future optimization of inversionless lasers.