Patent ID: 7423792
Filing Date: 2008-09-09
Classification: G03H

Abstract:
1. A dual mode holographic printer, said dual mode holographic printer being operable in a first mode of operation for directly writing a 1-step white-light viewable hologram and in a second mode of operation for writing a master hologram (H1) that is used thereafter to produce a white-light viewable hologram (H2), said holographic printer comprising: a pulsed laser source arranged to produce a laser beam at a first wavelength, said laser beam being split into an object beam and a reference beam which is mutually coherent with said object beam; an aperture arranged in the path of said reference beam and a reference beam lens arranged downstream of said aperture; a reference beam telescope arranged to control the size of said reference beam; a spatial light modulator wherein, in use, said object beam illuminates said spatial light modulator; a first lens system for writing a holographic pixel of said hologram on to a photosensitive medium, said first lens system being arranged downstream of said spatial light modulator and being arranged to focus said object beam to a minimum beam waist at a Fourier plane defined by said first lens system; positioning means for positioning said photosensitive medium at said Fourier plane in said first mode of operation and at a position downstream of said Fourier plane in said second mode of operation; and automatic spatial coherence varying means for automatically varying the spatial coherence of said object beam and for controlling the diameter of the object beam at said Fourier plane, wherein said automatic spatial coherence varying means comprises an adjustable telescope and a microlens array, said adjustable telescope comprising a plurality of lenses with a translatable lens mounted on a motorized translation stage, wherein said automatic spatial coherence varying means is arranged to automatically translate said translatable lens and wherein said adjustable telescope is arranged to create an approximately collimated variable diameter laser beam that illuminates said microlens array, said automatic spatial coherence varying means being arranged upstream of said spatial light modulator; wherein said reference beam lens arranged downstream of said aperture produces an approximate image of said aperture at the surface of said photosensitive medium.