Displacement measurement and surface profiling using semi-insulating photoconductive semiconductors and linearly frequency-ramped lasers

Target displacement measurement and surface profiling are demonstrated expe rimentally using coherence frequency domain reflectometry and the photo-emf optical difference frequency sensor that was recently shown to generate st eady state dc photocurrents linearly proportional to the optical frequency differences between two laser beams interfering inside semi-insulating phot oconductive semiconductors. The simplicity and spatial adaptivity of photo- emf optical frequency sensors eliminate the stringent requirements of optic al alignment and calculation-intensive signal processing found in conventio nal coherence frequency domain reflectometry systems. (C) 1999 American Ins titute of Physics. [S0003-6951(99)04436-8].