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Mid–infrared ‘W’ lasers

We review recent progress in the development of mid–infrared (mid–IR) quantum–well lasers with type–II antimonide ‘W’ active regions. Optically pumped W lasers achieved continuous–wave (CW) operation nearly to room temperature, and CW output powers exceeding 0.5 W per facet at 77 K. Improvements in the differential quantum efficiency were obtained by increasing the effective number of passes of the pump beam through the active region in the optical pumping injection cavity configuration. Near–diffraction–limited beam quality was achieved in the mid–IR using the angled–grating distributed feedback (α–distributed feedback (DFB)) approach with a W active region. Single–longitudinal–mode operation was demonstrated by vertical–cavity surface–emitting lasers emitting at λ = 2.9–3.0 μm. Broadened–waveguide W diode lasers recently operated at room temperature in pulsed mode and up to 195 K CW. A slope efficiency exceeding unity was achieved using the interband cascade laser approach with a W active region.