| 摘要 |
PURPOSE:To make secondary diffracted light brighter than the light by a diffraction grating which has a uniform grating constant by the setting change of a split light quantity ratio by providing diffraction grating parts which differ in a grating constant in the same grating. CONSTITUTION:The diffraction grating 1 consists of diffraction grating parts 2 and a diffraction grating part 3 while the grating parts 2 are arranged on both sides of the grating part 3 at the center part; and the split light quantity ratio is determined by slit width, slit intervals, and the area ratio of parts of the diffraction grating parts 2 and 3 which are irradiated with light beams. Here, when light with wavelength lambda is made incident vertically from below the grating 1, light which travels in the direction where asintheta=lambda and asintheta'=2lambda is generated to obtain primary diffracted light and secondary diffracted light. Here, (a) indicates the length between the centers of adjacent slits 4. Then when respective grating constants are so set that the secondary diffracted light and the primary diffracted light of the grating part 3 overlap with each other, the secondary diffracted light viewed from the grating 1 is brighter than the primary diffracted light (secondary diffracted light by a conventional diffraction grating). Therefore, this can be used to read data. |
