| 摘要 |
PURPOSE:To form easily and surely a diffraction grating having phase differences with a simple device by changing the optical path length of a transparent body to be placed between a light source and a medium for forming the diffraction grating and irradiating inclinedly luminous fluxes to the medium. CONSTITUTION:The medium 4 for forming the diffraction grating is provided and the transparent body 3 consisting of glass, etc. is imposed thereon. This transparent body 3 is provided with a step in the oscillation center part C so that the optical path lengths on both sides thereof vary. The two luminous fluxes 5 and 6 are irradiated via the transparent body 3 onto the surface of the medium 4. The luminous fluxes 5 and 6 are made incident at 2theta angle on the medium and the interference of the two luminous fluxes takes place on the medium 4. The two luminous fluxes 5 and 6 are irradiated in the asymmetrical state in which the central axis A constituted by the fluxes is inclined by the angle phi with the normal V. The phases of the interference fringes are consequently shifted with the step part 11 as the boundary. As a result, the phases of the diffraction grating 8 formed by exposing the interference fringes of the two luminous fluxes are also shifted with the step part 1 as the boundary.
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