Abstract

Interferometric testing of technical surfaces makes a reduction of the sensitivity necessary to deal with the rather big surface deformations and the micro-roughness due to the machining process. Therefore, grazing incidence interferometry is commonly used for planar work pieces. Here we report on the testing of cylindrical surfaces which makes use of computer generated holograms having cylindrical symmetry as beam splitters and recombining elements. The principle of the interferometer has been invented earlier/1/ and is given in Fig. 1. The collimated light beam from a laser impinges onto the first axicon-CGH and generates a first diffracted order which is reflected from the work piece and hits a second axicon CGH which combines the two beams reflected from the object and the undiffracted light of axicon 1 and 2. An ideal cylinder will result in a zero fringe field. All deviations from cylinder symmetry will be indicated through fringe distortions. Due to the diffractive axicons the deviation by one fringe corresponds to a surface deformation perpendicular to the surface of half a period of the axicon line pattern. In this way it is extremely simple to adapt the sensitivity of the interferometer to the technical needs. The deviations of the objects are somewhat screened by alignment aberrations.

© 1996 IEEE