Surface reconstruction based on transmission interferometric testing

A method of surface figure measurement is described based on the transmitted wavefront of an optical element obtained from a Mach-Zehnder interferometer. Given known values for the refractive index and center thickness, along with the samples transmitted wavefront, the unknown surface profile is reconstructed in a deterministic way. The technique relies on knowledge of one of the surfaces of the element, such as an easy to measure piano or spherical surface, and is well-suited for testing aspheric surfaces. Reverse raytracing is used to remove the effects of transmission through a thick lens and to remove induced aberration associated with the interferometer. In the interferometer, the wavefront transmitted through the sample is tested against a plano reference. In order to reduce the high frequency fringe content of the interferogram, the sample can be tested in an immersion solution. This method also has the ability to make measurements on multiplexed surfaces, such as a lenslet array, which traditionally can not be measured without moving the sample. The surface profile of a plano-convex lens has been produced and verified against other metrology techniques for calibration purposes. Surface measurements on a lenslet array are also presented.