TESTING OF ROD OBJECTS BY GRAZING-INCIDENCE INTERFEROMETRY - THEORY

Interferometry at grazing incidence allows one to perform macroscopic shape tests of rough surfaces with submicrometer precision. The highes t measurement accuracy is achieved with a null test: the object wave f ront is adapted to the ideal surface under test through the use of dif fractive optical elements. Deviations between the ideal and the real s urface shape result in characteristic phase distributions at the inter ferometer output. Rod objects with rather arbitrary cross-section prof iles are especially suitable for this type of measurement. The design of appropriate test wave fronts can be carried out by means of geometr ical considerations. Expressions describing aberrations that are due t o misalignments of the work piece can easily be derived. Misalignment aberrations and genuine surface deviations are separated by least-squa res fitting. (C) 1998 Optical Society of America. [S0740-3232(98)00411 -6]. OCIS codes: 120.3180, 050.1970, 050.2770, 050.1380, 090.1760, 220 .4840.