Real-time optical image subtraction

摘要

An apparatus for subtracting the amplitude of a first optical image on a first beam from the amplitude of a second optical image on a second beam includes a first beam splitter to divide the first beam into a first transmitted beam and a first reflected beam and to divide the second beam into a second transmitted beam and a second reflected beam. The first transmitted beam and the second reflected beam combine as a first mixed beam, while the first reflected beam and the second transmitted beam combine as a second mixed beam. A pinhole removes spatial information from the second mixed beam. The first and second mixed beams interfere within a nonlinear medium to create a composite hologram. A coherent reference beam directed at the nonlinear medium reads the interference pattern, so that the difference between the first and second images is superimposed on the reference beam emerging from the nonlinear medium. A second nonlinear medium may be used to retroreflect one of the mixed beams toward the nonlinear medium as the reference beam, in which case the pinhole is not required.