where is a constant phase due to the difference between the two optical paths, and are, respectively, the amplitude and the frequency of the phase modulation applied to object wave S. The two waves, R and S, interfere on the OASLM, thus inducing a phase grating in the liquid crystal layer. The total input field R + S crosses this thin phase grating undergoing a phase variation that is equivalent to a complex transmission. This latter can be written as
(