Midinfrared, optically pumped, unstable resonator lasers

The authors describe high-brightness, broad area midinfrared semiconductor lasers. These devices were fabricated in the authors’ laboratory using a commercial solid-source molecular beam epitaxial system. The laser structures incorporated 14 type-II quantum wells embedded in thick waveguide/absorber regions composed of ${\mathrm{In}}_{0.2}{\mathrm{Ga}}_{0.8}{\mathrm{As}}_{0.18}{\mathrm{Sb}}_{0.82}$ . The optically pumped devices achieved higher brightness operation as unstable resonators. Each unstable resonator was realized by polishing a diverging cylindrical mirror at one of the facets. For an unstable resonator semiconductor laser operating at $\sim 4.6\mu \mathrm{m}$ , near $84\mathrm{K}$ , and at a peak power of $6.7\mathrm{W}$ , the device was observed to be nearly diffraction limited at 25 times threshold. In comparison, a standard Fabry-Pérot laser was observed to be many times diffraction limited when operated under similar conditions.