The rotation method for the absolute testing of three flats is extended by adding a second rotation of one of the flats. This means that altogether five interferograms of pairs of flats (positional combinations) are evaluated: three basic combinations and two rotational combinations. The effect of random measuring errors is minimized by fully applying least-squares methods. Here the addition of a second rotation leads to a substantial increase of accuracy of the results and enables the lateral resolution to be further enhanced.
© 1993 Optical Society of America
Original Manuscript: July 29, 1991
Published: March 1, 1993
Günter Schulz, "Absolute flatness testing by an extended rotation method using two angles of rotation," Appl. Opt. 32, 1055-1059 (1993)