Enhanced nonlinear susceptibility in strained quantum cascade lasers

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Since the invention of the quantum cascade (QC) laser, which was demonstrated by Faist et al. in 1994, there has been much progress and advancement to include a wide range of wavelengths on GaAs and InP based material. Specifically, the operating range includes mid- to far-infrared with peak power levels in the watt range and above room temperature pulsed operation for wavelengths from 4.5 to 16 mum. There have been three distinctive designs of the QCL active region- the 'vertical' and 'diagonal' transitions and the 'superlatttice'- all of which are used with either surface-plasmon or conventional dielectric waveguides . Then, there is also the multiple wavelength superlattice, bi-directional, dual wavelength and the injector less quantum cascade lasers. With all the progress made thus far, there is still much work to be done in producing QC lasers that emit efficiently in the atmospheric window (3-5 mum wavelength range), which is important for free-space communications and gas sensing applications. Two known approaches in achieving QC lasers with shorter wavelength emission are through material selection, i.e. wider bandgap materials and type-II structures. There is an alternative approach that also holds much promise: exploitation of the nonlinear optical processes. Within the QC laser intracavity, higher order harmonic generation can be employed because both the fundamental and second-harmonic waves can propagate freely within the cavity without being reabsorbed by the semiconductor. Conveniently, the energy generated in this approach by the fundamental mode and second-harmonic generation is well below the selected material bandgap energy, which is still in the transparency region of the material. Appropriately, our work involves the study of strained active regions in AlGaAs/GaAs QC lasers with the goal of enhancing the nonlinear susceptibility and producing lasers that emit in the 3-5 mum wavelength range.