APPARATUS FOR MEASURING DIFFRACTION EFFICIENCY OF DIFFRACTION GRATING

PURPOSE:To make it possible to measure the diffraction efficiency of a diffraction grating highly accurately by one operation by providing a slide mirror which is slidden along an optical axis, a rotary stage which supports the diffraction grating to be measured and is rotated, and a switching mirror. CONSTITUTION:A diffraction grating 3 to be measured is arranged on a rotary stage 10. The light from a light source is reflected with a slide mirror 2 and a switching mirror 4 through a fixed mirror 1 as shown with a continuous line. The light is adjusted and measured with a photoelectric detector 12 so that the light intensity becomes 100. Then, the mirror 2 is moved along the optical axis from the mirror 1. The light from the mirror 1 is reflected to the grating 3 at a position 2'. The grating 3 generates 0-order diffracted light 20, first-order diffracted light 21... At this time, the first-order diffracted light 21 becomes the optical axis light 22. The light 22 is reflected at a position 4' and reaches the detector 12. The light intensity is measured as the diffraction efficiency. The light intensity is measured as the ratio between the light intensity which is measured through the path of the continuous line and the light intensity which is measured through the path of a dotted line. Since the lengths of the light paths are equal, the diffraction efficiency of the grating 3 can be measured highly accurately by one operation.