GB1311525A - Optical inspection method for optical element accuracy inspection - Google Patents

Abstract

1311525 Inspecting optical elements by holography CANON K K 31 March 1970 [31 March 1969 4 March 1970] 15138/70 Heading G2J A method for checking the accuracy of an optical element, for example a lens 14, comprises splitting a coherent wave into a test wave 15, whichis passed through the element; and a reference wave 11, directing the waves 11 and 15 on to an artificially prepared holographic test plate A and selecting waves radiated from the test plate to obtain an interference pattern. The test plate A is produced with an interference pattern such that if the element 14 has the required parameters, then the test wave emerging from the plate A resembles the reference wave so that if mirror 13 is tilted parallel equally-spaced fringes are obtained in the plane 18; if the element 14 deviates slightly from requirements the fringes are distorted. The waves emerging from the plate A are condensed by a lens 16 and the required diffraction orders selected by means of an aperture 17. Alternatively, Fig. 3 (not shown) the lens 16 may be omitted and the holographic test plate be a Fresnel zone plate (A'), so that the different orders of diffraction are concentrated at different distances from the test plate, Fig. 4 (not shown). The use of an artificially prepared holographic plate obviates the preparation of a master optical element and permits the preparation of complicated, e.g. non-spherical, surfaces.