New Procedures for the Adjustment of Elliptically Bent Mirrors with the Long Trace Profiler

摘要

Micro-focusing is widely applied at soft and hard x-ray wavelengths. One typical method, in addition to zone plates, is to split the focusing in the tangential and sagittal directions into two elliptically cylindrical reflecting elements, the so-called Kirkpatrick-Baez (KB) pair. In the simplest case each optic is made by grinding and polishing a flat, and applying unequal bending couples to each end. After briefly reviewing the nature of the bending, we show two new methods for optimal adjustment of these mirror systems using our surface normal slope measuring instrument, the long trace profiler (LTP). First, we adapt a method previously used to adjust mirrors on synchrotron radiation beamlines. We measure the slope of the surface before and after a single small adjustment of each bending couple. This permits an approximation to the functional dependence of slope on the adjustments, and allows, by applying the results of a simple matrix calculation, direct adjustment to a nearly final setting. Typically, the near linearity of the problem determines a very fast convergence of the adjustment procedure. Second, we subdivide the slope data from the LTP into three regions on the mirror, and fit a circle to each sub-region by regression. This method also allows rapid iterative adjustment of both bending couples. We show that this method is a particular case of the first one. As an overall indicator of predicted performance, we ray trace, using profiler data, predicting the exact optical performance to be expected during use of the system.