Photoresists
Photoresists are organic materials for producing thin relief phase holograms. Holograms in photoresist are ideal for making nickel masters which are used for embossing replicas.
Photoresists are of negative or positive working type. In negative working photoresist the unexposed areas are dissolved in the development, while in the positive working photoresist, the exposed areas are dissolved away in the developer. The negative working photoresist requires a larger exposure usually through the plate so that the expo sed photoresist adheres to the substrate during development.
The most widely used photoresist is Shipley Microposit 1350 which is a positive working resist. The sensitivity of this resist is maximum in the ultraviolet. It has adequate sensitivity at 458 nm of argon ion laser and 442 nm of He-Cd laser. However, the sensitivity at 488 nm is poor.
The material is coated on a glass substrate by spin method to a layer 1 to 2 micrometer thick. It is then baked at 75 deg C for 15 min. On exposure to light, the layer thickness changes.
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