Laser interference measuring of length device and its measuring of length error amendment manner

摘要

PURPOSE: To reduce the influence of a temperature by a method wherein an optical material in which a coefficient of thermal expansion and a refractive-index temperature coefficient are respectively positive and negative or negative and positive is used for a light-transmitting optical element through which reference light and measuring light are transmitted. ;CONSTITUTION: A laser beam from a light source 1 is separated by a beam splitter 2, separated beams are reflected respectively by a moving mirror 40 and a fixed mirror 50, the beams are superposed again by the splitter 2, and an interference is generated. Then, temperature changes from the initial state of the moving mirror 40 and of the fixed mirror 50 are designated respectively as ΔT_m and ΔT_f, the optical path length of the laser beams which are transmitted through both is designated both as L, and the coefficient of linear expansion, the refractive index and the refractive index temperature coefficient of both are designated respectively as α, (n), β. Then, a change ΔX in a length measured value due to a change in the optical path length L due to a temperature is expressed as ΔX=L{α(n-1)+β} (ΔT_m-ΔT_f)/2. Consequently, when ΔT_m=ΔT_f, the length-measured value is not changed. When they are not equal, the positive sign and the negative sign of the α and the β are mutually reversed, and the αand the β are offset. As a result, a length measuring error can be suppressed to be small.;COPYRIGHT: (C)1995,JPO