Surface dust blown by a lunar lander can spoof sensors and damage lander and other surface and orbital assets. Since many countries seek to use and leverage the Moon in the coming decades, this is potentially a defense issue. Empirical data on Plume Surface Interactions (PSI) from lander-mounted instruments are needed to determine particle size distributions. We report a feasibility study of laser light-scattering for particle sizing. Calculations suggest that distributions of particle sizes in the range 0.1 to 10 microns can be accurately determined from laser-propagation decay using 4 to 8 wavelengths between 0.4 to 2 microns. Lab standards have been created based on calibrated showers of silica spheres and known concentrations and sizes of SiC grit in resin rods. Experiments were performed using lasers from 0.4 to 10 micron wavelength. For visible wavelengths, a point Si detector or images taken with a Si CCD camera were used to record scattered intensity vs propagation distance. At long-wave infrared, a pyroelectric detector or bolometer array were used. Characteristic decay lengths were determined by an algebraic sliding aperture method suitable for rapid and automated analysis. The experiments confirm theoretical expectations for Mie scattering by simple distributions of spherical particles. These results inform future experiments for testing the inverse problem of extracting more complicated size distributions from decay lengths measured using multiple wavelengths.
Effects of gamma and proton irradiation, and of forward bias minority carrier injection, on minority carrier diffusion and photoresponse were investigated for long-wave (LW) and mid-wave (MW) infrared detectors with engineered majoritycarrier barriers. The LWIR detector was a type-II GaSb/InAs strained-layer superlattice pBiBn structure. The MWIR detector was a InAsSb/AlAsSb nBp structure without superlattices. Room temperature gamma irradiations degraded the minority carrier diffusion length of the LWIR structure, and minority carrier injections caused dramatic improvements, though there was little effect from either treatment on photoresponse. For the MWIR detector, effects of room temperature gamma irradiation and injection on minority carrier diffusion and photoresponse were negligible. Subsequently, both types of detectors were subjected to gamma irradiation at 77 K. In-situ photoresponse was unchanged for the LWIR detectors, while that for the MWIR ones decreased 19% after cumulative dose of ~500 krad(Si). Minority carrier injection had no effect on photoresponse for either. The LWIR detector was then subjected to 4 Mrad(Si) of 30 MeV proton irradiation at 77 K, and showed a 35% decrease in photoresponse, but again no effect from forward bias injection. These results suggest that photoresponse of the LWIR detectors is not limited by minority carrier diffusion.
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