New method for determining the transmitted wavefront error of interference filters

To assist in determining and tracking the transmitted wavefront error of the Canada-France-Hawaii Telescope filter stock, a method for determining the wavefront error, in transmission, of the filters using a white-light source has been investigated. The method uses the ef software from Laplacian Optics which determines a wavefront based on curvature sensing. The filter is placed in a collimated white-light beam. After the filter, the beam is imaged onto a small CCD which is placed on a translation stage. The CCD is moved to either side of focus to produce the two out-of-focus images required for curvature sensing. The results of this investigation compared to results using an interferometer will be presented.