| 摘要 |
PURPOSE:To enable high-accuracy alignment unaffected by position relationship by the absolute coordinates of two bodies, by irradiating two beams of monochromic light of two wave-lengths onto two diffraction gratings set on two bodies and measuring a phase difference of beat signals generated from respective grating. CONSTITUTION:Beams of monochromatic light of two wavelengths with frequencies slightly different one from the other are irradiated onto each of diffraction grating 32, 34 set on bodies 30, 31. Further, the gratings 32, 34 are so arranged that, they are deviated to the grating line direction avoiding overlapping in the plane view. There, light heterodyne interference diffraction beams generated from each grating 32, 34 are detected and beat signals are generated individually for measurements of the phase difference. Thus, the light heterodyne interference diffraction beams obtainable from the gratings 32, 34 respectively can be detected perfectly and independently one from the other. And, by detecting phase difference of the beat signals obtained from them, direct and stabilized detection of the phase difference corresponding to amounts of relative displacement of two bodies becomes available. Then, by zero-setting of the phase difference, a precision alignment can be conducted in a stabilized fashion. |
