To make it possible to form a diffraction grating which does not require intricate optical systems, has a simple phase shift and is modulated in period within the same substrate surface by recording the interference patterns formed by the interference of plus first-order diffracted light and minus first-order diffracted light formed from incident light by the diffraction grating on a photosensitive material.
The incident light 5 of a wavelength at which the photosensitive material 3 formed on a substrate 4 is sensitized is made incident on a transparent medium 2 formed with the diffraction grating 1 on its surface and the interference patterns formed by the interference of the plus first-order diffracted light 6 (θ+dif) and the minus first-order diffracted light 7 (θ-dif) formed by the diffraction grating 1 are recorded on the photosensitive material 3. The period of the interference patterns may be made 1/2 the period ΛM of the diffraction grating 1 without depending upon the wavelength λ and incident angle θin of the incident light 5 by using the interference of the plus first-order diffracted light 6 and minus first-order diffracted light 7 formed by the diffraction grating 1 in such a manner. As a result, the formation of the diffraction grating 1, i.e., master diffraction grating to be disposed at the transparent medium 2 is facilitated.
