James S. Swenson

Enhanced mass‐transport smoothing of f/0.7 GaP microlenses by use of sealed ampoules

A variety of GaP lens arrays have been routinely produced (array dimensions up to 1.5×1.0 cm, 30×50 elements) with high yield, uniformly good finish, and low transmission loss for 0.8 μm<λ<2.5 μm. Microlenses up to 300 μm in diameter with f numbers as low as 0.7 have been fabricated by a new sealed ampoule mass‐transport technique. The mesa‐step spacing was increased from 10 to 15 μm, with mass‐transport smoothing time‐at‐temperature as short as 8 h, representing a transport‐rate 10–40 times higher than previously reported. By additional chemistry control, smoothing of 30 μm spacings has been demonstrated. Only small pieces of phosphorus are required (no phosphine or hydrogen), consequently little safety burden is incurred. Smoothing in the fused quartz ampoules is shown to be self‐terminated by wafer oxidation, which is sufficiently delayed by loose‐fitting aluminum oxide shielding.

Single-frequency low-threshold continuous-wave 3-μm periodically poled lithium niobate optical parametric oscillator

A low-threshold (350-mW) stable single-frequency continuous-wave optical parametric oscillator was demonstrated. Tunable idler output up to 450 mW was obtained near 3 μm by resonating both the signal wave and a single-frequency 1.06-μm Nd: YAG pump laser in a periodically poled lithium niobate optical-parametric-oscillator ring resonator. Tunable output wavelengths from 2.9 μm to 3.25 μm were also demonstrated. By inserting an etalon, we achieved an absolute midinfrared single-frequency stability of +/-0.01 nm.

High-efficiency longitudinal diode bar pumping of solid state lasers

A longitudinal diode bar pumping scheme for a solid state laser has been conceived which can concentrate tens of watts of pump power into a 300 micrometers spot with 90 to 95% efficiency.

Flight of the pico satellite solar cell testbed (PSSC Testbed) space experiment

The PSSC Testbed flight data confirmed that the picosatellite can be used for measuring I–V characteristics of solar cells. Continuing monitoring of the I–V measurement will allow determining the actual degradation of the solar cells due to exposure to the space environment. Mission success for the initial low earth orbit (LEO) space flight provided proof of concept for the PSSC Testbed. Subsequent mission will fly in a geosynchronous transfer orbit (GTO), in which a 450-day radiation exposure of the solar cells will be equivalent to that of 15 years radiation exposure in geosynchronous orbit.

Solar cell calibration for the Pico Satellite solar cell testbed (PSSC Testbed) space flight experiment

The results of this preflight calibration of the measurement electronics and the individual solar arrays will allow corrections to be made to flight data for determining the actual degradation of the test solar cells as a result of exposure to the space environment.

Fabrication of f/0.7 GaP microlens arrays by accelerated mass-transport smoothing in sealed ampoules

GaP lens arrays have been routinely produced in large formats (substrate dimensions up to 1.5 by 1.0 cm) with high yield and uniformly good finish. Diffraction-limited performance for collimation of single-mode diode lasers has been demonstrated. Laser-diode bars and coherent 2-D surface-emitting arrays have also been collimated with low transmission losses (98%) for 2.5 micrometers > (lambda) > 0.8 micrometers . Microlenses up to 300 micrometers in diameter with f/#s as low as 0.7 have been enabled by a new mass transport fabrication technique using sealed quarts ampoules rather than a flowing tube furnace. In this modification only small pieces of phosphorus are required (no phosphine or hydrogen); consequently, little safety burden is incurred, and initial expenses are reduced. The mesa-step-spacing was increased from 10 micrometers to 15 micrometers , and, by additional chemistry control, 30 micrometers spacings have been demonstrated. Also, time-at-temperature for mass-transport smoothing has been shortened to as little as 8 h. Mass-transport chemical mechanisms and material incompatibilities are discussed. Smoothing in the fused-quartz ampoules is shown to be self- terminated by wafer oxidation, probably caused by oxygen from thermal equilibrium dissociation of the silicon dioxide ampoule. This mass transport technique lends itself to a wide variety of novel lens fabrication strategies and clearly extends the potential applications.