Mid-wave infrared and terahertz quantum cascade lasers based on resonant nonlinear frequency mixing

Abstract

GaInAs/AlInAs/InP quantum cascade lasers (QCLs) have established themselves as reliable and versatile semiconductor laser sources in the mid-infrared wavelength region. Due to the presence of unique molecular absorption lines, in combination of water-free atmospheric transmission windows, this spectral range is of particular importance for sensing, medical, material processing and homeland security applications. Being compact electrically pumped and able to operate at room-temperature, QCLs are ideal choice for wavelengths between 3.5 - 12 microns. However, wavelengths above and below are more challenging to obtain. In our work, we use intracavity nonlinear frequency mixing in mid-infrared QCLs to extend the spectral coverage for GaInAs/AlInAs/InP devices. We demonstrate that passive nonlinear structures, consisting of coupled quantum wells can be grown on top of the mid-IR QCL active region. Such nonlinear structures can be designed to possess a resonant nonlinear response for the pump frequency. Such concept, in combination with quasi-phase-matching technique can be used for efficient short-wavelength lasing by second-harmonic generations. We demonstrated room-temperature lasing down to 2.6 micrometer. For long-wavelengths, particularly THz frequencies, a novel waveguide concept was introduced. Here, we used a leaky THz waveguide concept, for a difference-frequency generation device. Phase matching was achieved by Cherenkov phase-matching scheme. This concept led to ultra-broadband THz emission at room-temperature (1.2-4.5 THz) with pulsed output powers as high as 14 μW.