Master hologram and micropattern replication method

A method of recording a microscopic surface relief pattern corresponding to the amplitude of a radiation field of interfering coherent waves, such surface relief pattern having variations of surface height below approximately one micron, wherein the method comprises the steps of

• (A) providing a field of interfering coherent waves
• (B) providing a smooth silver surface, and
• (i) chemically sensitizing the silver surface to radiation by reaction with a halogen to form a silver halide at said surface and subsequently
• (ii) exposing the surface to said field of interfering coherent waves so as to dissociate the silver halide and thereby form a chemically varying surface distribution in a pattern corresponding to variations in amplitude of said field and
• (iii) selectively removing material from said surface by differentially etching said chemically varying surface distribution to achieve a corresponding pattern having differential surface relief which transforms the phase of coherent light reflected from said surface in accordance with the interfering coherent waves.

A method of making a holographic pressing master for embossing a desired phase hologram such method comprising the steps of:

• (i) providing a polished silver plate,
• (ii) sensitizing the plate by chemically reacting a halogen at the surface thereof to form a photodissociable halogen salt at the surface
• (iii) exposing the sensitized plate to a coherent light field to dissociate the silver halide in exposed areas and thereby vary the surface composition of the silver plate in accordance with the amplitude of said coherent light field over the surface, and
• (iv) etching the plate with an etchant which differentially etches different portions of said varying surface composition to produce a relief modulated surface corresponding to said desired phase hologram, said etching being carried out to a relief depth sufficient for embossing phase hologram copies therefrom.

A method of recording a pattern of electromagnetic radiation so as to make a master pattern having a surface for modulating electromagnetic radiation in accordance with said master pattern, such method comprising the steps of

• (i) providing a substrate having a smooth silver surface,
• (ii) chemically treating the surface to form a radiation sensitive silver halide skin thereon by chemical reaction of a halogen with the silver surface,
• (iii) exposing said skin to a recording pattern of said electromagnetic radiation, and
• (iv) further treating the exposed skin to remove an effective amount of material therefrom to form said master pattern for phase modulating electromagnetic radiation directed thereat.