Abstract: A holographic objective system (3) produces an intermediate real image (4) of information displayed on an electrically addressable spatial light modulator or SLM (1), the real image (4) being collimated by a powered holographic reflector (5) constructed as part of the visor of a helmet worn by the viewer (9). The SLM (1) is illuminated by laser light from a remote laser (8) via a single optical fibre (6) and beam splitter (2). A diffuser (7) is provided either between the laser and the beam splitter or in the plane of the intermediate image (4). The objective system (3) may alternatively include, or consist entirely of, conventional optical elements.

Abstract: A color selective filter in the form of a holographic reflector is produced by a method which includes the step of exposing a photosensitive film of gelatine to a monochromatic laser beam. In order to obtain acceptably short exposure times and to enable substantially the whole of the available laser light to be utilized, a relatively narrow laser beam is sequentially scanned across the surface area of the gelatine film in a scanning pattern which consists of a large number of parallel straight lines. The diameter of the laser beam spot is very large as compared with the spacing between adjacent line scans. In this way each point on the gelatine film is scanned a very large number of times.The laser beam 8 is generated by a laser 7 and deflected by two movable mirrors 10 and 11, which are controlled so that the beam scans the whole of the gelatine film 1.