Post-polish figuring of optical surfaces using multilayer deposition

Abstract

We present preliminary results of a technique that uses deposition of variable-thickness multilayer films to correct optical figure errors. The multilayer technique offers the potential to make figure corrections, such as aspherizing high-quality spherical optics, without adding measurable roughness. Moreover, because the period of a multilayer can be measured very accurately using x-ray diffraction, we can easily map test depositions made on inexpensive float-glass substrates. We have used this technique to reduce large rotationally symmetric errors by almost an order of magnitude in a single run. Extension to the correction of non-symmetric errors was performed by deposition through a two-dimensional mask, which was less successful. We have identified several sources of error in this type of deposition and discuss means of improvement. We have devised a method using a series of rotationally-symmetric masks and a varying-rotation-rate substrate stage to reduce the two-dimensional problem to a series of one-dimensional problems.