Process for producing a diffraction grating

Details Process for producing a diffraction grating Process for producing a diffraction grating

1980-09-12

1983-09-13

Arnold, Bruce Y.

350320, G02B 518

Patent

active

044038275

ABSTRACT:
A diffraction grating is formed by depositing a glass film on a substrate and thereafter applying to the glass film a layer that is highly absorptive to radiation of a specific wavelength. The highly absorptive layer is then coated with a photoresist that is transparent and photosensitive to light of the specific wavelength. Next the photoresist layer is exposed with a holographic image of a desired grating pattern, and the exposed areas are carried away in a developing solution, leaving the photoresist with a grating pattern consisting of a series of closely spaced ridges separated by voids. During the exposure of the photoresist, the absorbing layer absorbs most of the radiation that penetrates the photoresist and thereby prevents that radiation from reflecting from the glass layer or the substrate and creating a pronounced standing wave pattern. A wave pattern of that nature would expose the photoresist in undesired areas, resulting in weakened ridges during the subsequent development. By reducing the standing waves, unusually high ridges are obtained. Thereafter, the deep grating pattern is transferred to the glass film by ion-milling the exposed surface of the photoresist. This erodes both the photoresist and the glass film, and due to the deep grating pattern in the photoresist, the grooves imparted to the glass film are also quite deep. The greater depth of the grooves in the glass significantly improves the diffraction efficiency.

REFERENCES:
patent: 2927023 (1960-03-01), Martin
Lehmann, Matt, "Fabrication of Metallic Gratings on Photoresist by Holographic Recording", Conference & Proceedings of the Engineering Applications of Holography Symposium, Los Angeles, Calif., Feb. 16-17 1972, pp. 327-330.

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