Browse Prior Art Database

Thermally Induced Surface Relief Holograms

IP.com Disclosure Number: IPCOM000039942D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Brady, MJ: AUTHOR [+2]

Abstract

Holograms on photoresist are recorded as surface relief modulations (SRH), as opposed to phase holograms which are refractive index modulations. Fabrication of SRH requires a layer 10 of resist, which is then exposed to the sinusoidal intensity distribution resulting from the interference of two mutually coherent laser beams 12, as depicted in the figure. Wet development transforms exposure variations into surface modulations in the resist, which in turn cause periodic phase changes giving rise to a diffraction pattern. Parameters that control diffraction efficiency, that is, the amount of incident illumination that is diffracted into the first order, are the wavelength-to-grating period ratio (go/d), and the ratio of modulation depth to period (h/d).

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Thermally Induced Surface Relief Holograms

Holograms on photoresist are recorded as surface relief modulations (SRH), as opposed to phase holograms which are refractive index modulations. Fabrication of SRH requires a layer 10 of resist, which is then exposed to the sinusoidal intensity distribution resulting from the interference of two mutually coherent laser beams 12, as depicted in the figure. Wet development transforms exposure variations into surface modulations in the resist, which in turn cause periodic phase changes giving rise to a diffraction pattern. Parameters that control diffraction efficiency, that is, the amount of incident illumination that is diffracted into the first order, are the wavelength-to-grating period ratio (go/d), and the ratio of modulation depth to period (h/d). The first parameter, go/d, is determined by the recording wavelength and the angle 2r formed between the two recording wavefronts. The second parameter, h/d, is controlled by exposure and processing variables. Standard resists require wet development processing following exposure. In general, wet processing requires tight controls. Since the process window is narrow, in-situ monitoring of development ____ processes is required, as well as monitoring of the development concentration, temperature and pH, as these parameters tend to modify the response of the resist. A technique is described that eliminates "wet" processing, provides a wider process window, and allows good con...