Abstract
The use of surface relief structures is increasing in the field of optics. A study of photoinduced relief using dichromated gelatin films with different thickness is described in this paper. Two light sources were used: a laser (λ = 468 nm) and an ultraviolet mercury-metal halide lamp. Gratings with low spatial frequencies were contact-copied on the DCG (dichromated gelatin) films. Two development processes were used, one included washing the plates with just water and the other with a mixture of water and papain. This enzyme is used to improve the gratings’ relief which was studied with a profilometer. For the development process with just water, it was found that when gratings were recorded using visible or UV light, the height profile inversely correlated to spatial frequencies. For short exposure times, the reliefs showed a sinusoidal profile. When visible light was used, the DCG areas where the Ronchi grating had transparent slits showed a flat relief and the areas where the Ronchi grating had opaque slits showed a round peak, with the peak being taller than the flat surface. In contrast, when UV light was used, the flat surfaces were taller than the peaks. The relief height increased up to seven times when papain was used.
Highlights
Since the 1800s, dry films of chromates and dichromates mixed with organic materials such as gelatin, fish glue, gum arabic, or shellac were known to be affected by light [1]
In 1968, Shankoff [2,3] proposed the use of dichromated gelatin plates (DCG plates) as the material to record holograms
DCG plates can be made with gelatin and dichromates or with Kodak 649 F plates used as gelatin films where the silver halide has been removed with the development and fixing process
Summary
Since the 1800s, dry films of chromates and dichromates mixed with organic materials such as gelatin, fish glue, gum arabic, or shellac were known to be affected by light [1]. Besides DCG plates, other materials have been used to fabricate optical relief elements, such as albumen [4], acrylamide dry films [5], polyacrylamide wet films (used to record transient interference patterns) [6], silicone [7,8], gelatin [9,10], liquid resins [11], and silver halide plates [12,13,14,15,16,17,18]. The analysis of these aspects was partially performed and reported in references [12,13,14,15,16,17,18], using DCG films In these works, spatial frequencies between 60 and 200 L/mm are used, and the reliefs generated are approximately 0.4 μm to 1.4 μm thick, with a development step with water and a postprocessing method with UV light.
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