Preparation of damage resistant optical coatings on flat substrates

A list of all the rugate filters that were made with the planar high temperature PICVD coater and shown to LLNL during the visit of Otto to Livermore in November 1990 are included. Those samples that have been left at LLNL are indicated. The process parameters are also added. It was demonstrated that the planar high temperature PICVD coater is in principle capable of making high reflectivity rugate mirrors. A deposition rate of up to 1.44 {mu}m/min was obtained and thick layers (475 {mu}) with over 1000 periodes could be made. The deposition turns out to be non-uniform across the substrate with respect to reflectivity, band shape, peak width and film thickness. There are two types of thickness non-uniformities: bumps caused by a too small spacing between substrate and shower head, and an overall non-uniformity due to a marginal effect. The non-uniformity in reflection is probably due to a non-uniform feeding of microwave power into the plasma. It is therefore necessary to search for an improved antenna design to overcome the uniformity problems. The damage thresholds of all the coatings made with the flat coater turned out to be much lower (<20 J/cm2) than for PICVD coatings in cylindrical geometrymore » (in tubes up to 63 J/cm2) for unknown reasons. Possible measures for a reduction of the number of particulates in the films are discussed. 11 figs., 4 tabs.« less