| 摘要 |
PURPOSE:To make positioing with high stabilizing accuracy at all times independently of the size of an object to be positioned, by vertically irradiating a plurality of coherent lights with different wavelengths to a diffraction grating and detecting diffracted light on the diffraction grating. CONSTITUTION:When lasers 21 and 22 with different wavelengths are irradiated on diffraction gratings 14 and 18, coherent lights 23 and 24 having the intensity corresponding to the extent of shift of the diffraction gratings 14 and 18 are detected at photodetectors 27a, 28a and 27b, 28b located respectively toward (+n) and (-n) order direction and the lights are converted into photodetection signals. Each photodetection signal are given to operational amplifiers 31 and 32 to obtain a difference between the lights with equal wavelength. Each difference signal is square-averaged at an operation circuit 33. The output represents the extent of shift of positioning for an object to be positioned. |
