A holographic grating is made by exposing micro-grain film to two interfering He-Ne laser beam (λ=0.6328μm, 5mw, 3cm diameter).
The holographic grating is bleached ($Ag \Rightarrow Agcl$) to be a phase grating.
Two images to be added or subtracted are mounted on the front focal plane of Fourier transform lens, and on the back focal plane the phase grating is mounted.
With slight displacement of the phase grating in the direction perpendicular to the optical axis, added and subtracted images are obtained simultaneously on the back focal plane of inverse Fourier transform lens.
In the present optical system, both amplitude and phase image subtractions are obtained. Also, in this work conversion of phase image to amplitude image, elimination of background exposure and inversion of contrast are achieved.
