COMPUTER-GENERATED HOLOGRAM (CGH), AND METHOD FOR CHARACTERISING THE SURFACE FORM OF AN OPTICAL ELEMENT

摘要

The invention relates to a computer-generated hologram (CGH) and a method for characterising the surface form of an optical element. In accordance with one aspect a CGH has a first region (121, 321, 421) having a useful structure (A) and a second region (122, 322, 422), which is spatially separate from said first region (121, 321, 421), the second region forming a monitoring region for detecting contamination forming on the CGH (120, 320, 420, 520).