METHOD OF MAKING A DIFFUSING LAYER

1312717 Diffusion device for holography AGFA-GEVAERT AG 13 April 1970 [11 April 1969] 17533/70 Heading G2J A diffusion device which eliminates granulation effects when used to illuminate a transparent photographic image which is to be holographed, is manufactured by recording in a photo-sensitive medium a section through a light beam having a desired phase distribution, then treating the medium in a bleaching bath so that the spatial variations in phase of the beam are recorded as variations in the optical path length through the medium in a given direction, so that the medium is of uniform optical density and so that the optical path length variations are less than half the wavelength of the light used in making a hologram. In addition to the bleaching treatment, whereby the part of the medium containing a record of the light beam is converted to a dielectric substance having a refractive index different from the surrounding medium, this part may be treated so that the thickness of the medium varies spatially to correspond to the record.