| 摘要 |
PURPOSE:To improve positioning accuracy by irradiating two places of an object of measurement in the direction of displacement measurement with laser beams coaxially and taking measurements simultaneously at the two places. CONSTITUTION:A laser beam 22 for measurement is split by a beam splitter in X and Y directions and made incident on 50% beam splitters 39 and 40. The laser beam which is made incident on the beam splitter 39 is split into two directions; and one is made incident on an interferometer 251 and the other is made incident on an interferometer 252 through beam benders 41 and 42 respectively. The laser beam which is made incident on the beam splitter 40, on the other hand, is split into two directions; and one beam is made incident on an interferometer 253 and the other is made incident on an interferometer 252 through beam benders 43 and 44 respectively. Consequently, the interferometers 251 and 252 which face reflecting surfaces 38a and 38b measure X-directional displacement and interferometers 253 and 254 facing reflecting surfaces 38c and 38d measure Y-directional displacement, so that the quantities of displacement of the object of measurement in the X and Y directions can accurately be measured. |
