| 摘要 |
PURPOSE:To have a substantial thickness and to enable provision of efficient convergency to a plane lens by exchanging the lithium ion in a lithium niobate base plate provided with a mask consisting of titanium or chromium and the hydrogen ion in benzoic acid. CONSTITUTION:A plane photoconductive layer 12 obtd. by thermal diffusion of metallic titanium is provided on the surface of a lithium niobate base plate 11 and a lens pattern 21 of photoresist reversed by an ordinary photolithography technique is formed thereon. A titanium film 22 is then provided on the pattern 21 by a vapor deposition method or the like. The pattern of the film 22 formed in the above-mentioned way is the reversal of the resist pattern and eventually the mask having the aperture in the shape of the lens pattern is obtd. When the base plate is further immersed for specified time with the film 22 as a mask in a soln. 23 in which benzoic acid is dissolved, ion exchange is effected in the aperture part of the mask and the film 22 on the surface is removed by a hydrofluoric acid or the like, by which the plane Fresnel lens is completed. |
