SHAPE MEASUREMENTS OF MIRROR SURFACES WITH A LATERAL-SHEARING INTERFEROMETER DURING MACHINE RUNNING

A common path lateral-shearing interferometer with a minimum number of optical components has been developed. Because the interferometer is little affected by mechanical vibrations and air turbulence, it can be mounted on an ultraprecision lathe and can be used to measure the sha pes of workpieces. A plane parallel glass plate is used to shear the w avefront under test in the interferometer. To analyze the interference fringes obtained by the interferometer precisely, a fringe-scanning m ethod using a slight tilt of the glass plate is used. Zone plates that are computer-generated holograms are used to measure spherical and as pherical surfaces with the interferometer. A spherical and a parabolic concave mirror were measured with the interferometer. The spherical m irror was also measured by a Fizeau interferometer to compare the erro r with that measured by the lateral-shearing interferometer. The exper imental results agreed well with those measured by the lateral-shearin g interferometer. (C) 1998 Elsevier Science Inc.