David J. Gallant

High‐power spatially coherent operation of unstable resonator semiconductor lasers with regrown lens trains

We have obtained high‐power spatially coherent operation in wide‐stripe InGaAs/GaAs/AlGaAs semiconductor lasers using a monolithic unstable resonator [consisting of diverging lens elements incorporated above an asymmetric graded‐index separate confinement heterostructure (AGRIN‐SCH)]. The fabrication involves MOCVD regrowth after wet‐chemical etching of lens‐like patterns in a GaAs layer above the active region. Pulsed output powers of 175 and 490 mW have been obtained in 170‐ and 100‐μm‐wide lasers, respectively, with spatial coherence in the near field exceeding 60%. We observe good lateral mode discrimination up to 3.5 times threshold in the 100‐μm stripes with a round‐trip magnification of 6.4.

Novel high‐power and coherent semiconductor laser with a shaped unstable resonator

We describe a novel high power semiconductor laser that employs a shaped unstable resonator waveguide to maintain fundamental spatial mode operation at high power levels. We call this device the SHUR (shaped unstable resonator) laser. By photoetching and regrowth we locate a secondary, nonplanar antiguide, beneath the main part of the waveguide. The lasing mode couples to this secondary guide and experiences lateral antiguiding, which is the basis of the unstable resonator action. Prototype versions of the SHUR laser show a maximum pulsed output power of 770 mW per facet. The focused beam is dominated by a single lobe that contains 47% of the output power.

Semiconductor laser with unstable resonator consisting of negative cylindrical lenses

We have obtained high power single-lateral-mode operation in wide-stripe InGaAs/GaAs/A1GaAs semiconductor lasers using a monolithic unstable resonator (consisting of diverging elements incorporated above an asymmetric GRIN-SCH). The fabrication involves MOCVD regrowth after wet-chemical etching of lens-like patterns in a GaAs layer above the active region. Pulsed output powers of 175 mW and 490 mW have been obtained in 170 p.m and 100 tm wide lasers respectively, with spatial coherence in the near-field exceeding 60%. We observe good lateral mode discrimination upto 3.5 times threshold in 100 .tm stripes with a round-trip magnification of 6.4.

Simulation of semiconductor lasers with quasi-continuous unstable resonators and comparison with experimental data

Data from regrown-lens-train lasers are used to validate a computer program for their simulation. Curves of light output as a function of current have been calculated and compare well with experimental data taken for three lasers with widely varying geometries. The optimum reflectivity of the front facet of a laser with a high-reflectivity back facet is calculated, and the output power is about the same as was obtained for the double- facet output of the experimental laser with uncoated facets. The power loss due to the finite width of the lenses is estimated.

Instrumentation For Optical Characterization Of Laser Optics

For several years, the Optical Component Evaluation Laboratory (OCEL) and three sister laboratories have been building and operating optical measurement equipment. This contractual work is being done at Kirtland Air Force Base, New Mexico. Optical measurement capabilities include reflectance, transmittance, scatter, and laser absorption at one or more wavelengths including 351, 442, 633, 514, 1064, and 1318 nm.