Type-I QW cascade diode lasers for spectral region above 3 μm

Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of GaSb-based diode lasers operating in spectral region from 3.1 to 3.3 μm. The experiment showed that the increase of the number of cascades from two (previously used in record cascade 3 μm emitters) to three led to critical enhancement of the differential gain and reduction of the threshold current density of λ > 3 μm lasers. Light p-doping of the AlGaAsSb graded section did not introduce extra optical loss but aided hole transport as required for realization of the efficient multi-stage cascade pumping scheme. Corresponding coated three-stage devices with ~100-μm-wide aperture and 3-mm-long cavity demonstrated CW output power of 500 mW near 3.18 μm at 17 °C – more than twofold increase as compared to previous state-of-the-art diode lasers emitting only 200 mW. Three-stage lasers with quantum wells designed to emit in the middle of methane absorption band near 3.25 μm demonstrated record output power levels above 350 mW – nearly threefold improvement over previous non-cascade state-of-the-art diodes. Utilization of the different quantum wells in cascade laser heterostructure was demonstrated to yield wide gain lasers as often desired for tunable laser spectroscopy. Two step etching was applied in effort of simultaneous minimization of both internal optical loss and the lateral current spreading in narrow ridge lasers.