INTERFEROMETRIC STRAIGHTNESS MEASUREMENT SYSTEM USING TRIANGULAR PRISMS

A new interferometric system for measuring straightness is developed. In the system, triangular prisms are used to generate two converging b eams. A straightness reflector is used to reflect back the converging beams along their respective paths to form a combined beam. The combin ed beam is received by a detector system to count the interference fri nges. Being different from the traditional straightness reflector, the new straightness reflector consists of not only reflecting surfaces b ut also refractive surfaces. The refractive surfaces cause a change in optical path difference (OPD) when a relative lateral displacement be tween the triangular prisms and the straightness reflector takes place . The relationship between the OPD and the lateral displacement is der ived. The expected results agree with the results in the experiments. A straightness measurement with an accuracy of 0.1 mu m is obtained ov er a travel range of 120 mm. (C) 1998 Society of Photo-Optical Instrum entation Engineers. [S0091-3286(98)00706-5].