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 In0.2Ga0.8As0.18Sb0.82. 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 ∼4.6μm, near 84K, and at a peak power of 6.7W, 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.