Mid-infrared 'W' lasers

We review recent progress in the development of mid-infrared (mid-IR) quant um-well Iasers with type-II antimonide 'W' active regions. Optically pumped W lasers achieved continuous-wave (CW) operation nearly to room temperatur e, and CW output powers exceeding 0.5 W per facet at 77 K. Improvements in the differential quantum efficiency were obtained by increasing the effecti ve number of passes of the pump beam through the active region in the optic al pumping injection cavity configuration. Near-diffraction-limited beam qu ality was achieved in the mid-IR using the angled-grating distributed feedb ack (alpha -distributed feedback (DFB)) approach with a W active region. Si ngle-longitudinal-mode operation was demonstrated by vertical-cavity surfac e-emitting lasers emitting at lambda = 2.9-3.0 mum Broadened-waveguide W di ode lasers recently operated at room temperature in pulsed mode and up to 1 95 K CW. A slope efficiency exceeding unity was achieved using the interban d cascade laser approach with a W active region.