| 摘要 |
PURPOSE:To easily obtain plural diffraction grating which has different periods by performing exposure once by utilizing a polygonal mirror as a reflection mirror for an interference exposing method in the formation of the diffraction gratings. CONSTITUTION:Part of light incident on polygonal mirrors 6 and 7 becomes light beams (d) and (e) to form interference fringes with a period lambda0/2sinalpha on the surface of a substrate 5 as usual. The remainder of the incident light is reflected by the other surfaces of the polygon mirrors 6 and 7 having a tilt angle beta to become light beams (f) and (g) having an angle 2beta in an x-z plane. Interference fringes with a period lambda0/2sinealphacos2beta are formed on the surface of the substrate 5 by the interference between the light beams (f) and (g). Thus, the polygonal mirror 6 and 7 are utilized to obtain plural interference fringes having different period by one-time exposure.
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