SPIE Proceedings [SPIE IS&T/SPIE Electronic Imaging - Burlingame, California, United States (Sunday 22 January 2012)] Sensors, Cameras, and Systems for Industrial and Scientific Applications XIII - Development of high-transmittance back-illuminated silicon-on-sapphire substrates thinned below 25 micrometers and bonded to fused silica for high quantum efficiency and high resolution avalanche photodiode imaging arrays