1. V. Dose, Rev. Sci. Instrum. 39, 1055 (1968)
2. V. Dose, Th. Fauster, and R. Schneider, Appl. Phys.A40, 203 (1986).
3. CaF2 and SrF2 windows are available from Harshaw Optical/Bicron, 6801 Cochran Road, Solon, OH 44139.
4. The vacuum cement used is Araldit AT1, Ciba-Geigy GmbH, Oeflinger Str. D-79664 Wehr (Baden), Germany.