We describe a variation of the liquid-flat technique for determining the absolute flatness of a 240-mm-diameter optical surface to an accuracy better than 1/100λ in both its horizontal (three-point support) and vertical orientations. Using the appropriate mathematics to calculate the surface deformation of a disk due to gravity, we achieved verification of the method by comparing measurements carried out on a pair of optical flats and a liquid reference surface.
© 1998 Optical Society of America
Original Manuscript: May 12, 1997
Revised Manuscript: July 10, 1997
Published: May 1, 1998
Ian Powell and Emmanuelle Goulet, "Absolute figure measurements with a liquid-flat reference," Appl. Opt. 37, 2579-2588 (1998)