Surface-Emitting, Monolithic Beam-Combined Mid-Wave IR Quantum Cascade Lasers

The technical objectives of this proposal are: (1) design a grating-coupled surface-emitting (GCSE) active-photonic-crystal (APC) 4.6 micron-emitting quantum-cascade laser (QCL) to deliver 15 W diffraction-limited CW power in the main lobe of the far-field beam pattern; (2) design a GCSE-APC QCL structure with monolithic aperture-filling optical elements for obtaining close to 90 % of the surface-emitted power into the main lobe of the far-field beam pattern; and (3) design a GCSE-APC QCL structure employing second-order gratings with chirped period for increasing the light-outcoupling efficiency and the device wallplug efficiency. Step-taper-active (STA) QCLs will be used in the design since they suppress carrier leakage out of the QCL active regions, resulting in electro-optic characteristics much less temperature sensitive than for conventional QCLs; thus, allowing for significant increases in CW power and wallplug efficiency. The design will be for APC devices of built-in index step an order of magnitude higher than for conventional APC-QCL as to achieve stable-beam operation in CW operation to high coherent powers with high wallplug efficiency. For 4.6 micron-emitting devices the design will be for usable CW powers as high as 20 W, delivered in diffraction-limited beams.