Submicron entrance windows for an ultrasoft x‐ray camera

During the development of an imaging proportional counter suited for observing celestial objects in the XUV waveband (10–250 Å), we investigated the feasibility of producing a reliable plastic entrance window having a thickness ⩽ 0.3 μ and good uniformity over an area of several tens of square centimeters. After evaluating several candidate materials and production techniques, we selected film casting of pure Lexan as an appropriate technique for providing strong 65 mm diameter, 0.3‐μ thick windows having low gas diffusion leakage (