Surface dust blown by a lunar lander is a threat to operations and assets. Multi-national lunar exploitation makes this a potential defense problem. To aid prediction and protection, we are developing a lander-mounted laser-based instrument to obtain empirical particle-size distributions in ejecta plumes. The method is based on analysis of laser propagation decay at multiple wavelengths. System design depends on expected laser propagation decay lengths in the cloud of lunar particles lofted by the lander rockets. We present laboratory experiments to confirm theoretical expectations for laser propagation decay constants for independently known particle size distributions. The method of extracting particle size distributions from measured decay constants at multiple wavelengths is demonstrated. Predictions are made for decay constants in lunar plumes with representative regolith size distributions and minerology.
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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