Photoconductive semiconductors that contain deep-level traps can be us
ed as optical phase detectors because of photocurrents generated by mo
ving space-charge electric fields formed inside the material by transi
ent optical interference patterns. Two narrow-linewidth Nd:YAG nonplan
ar ring oscillator lasers were successfully phase locked with InP:Fe,
GaAs:Cr, GaAs, and CdTe:V crystals used as optical phase detectors.