Total cross sections for metastable excitation in the rare gases

Optical characterization of a compact multilayer-mirror polarimeter in the extreme-ultraviolet range

A molybdenum-silicon (Mo/Si) multilayer-mirror (MLM) polarimeter has been constructed and used to analyze the extreme-ultraviolet (EUV) emission from excited HeI and HeII states following electron impact on He for wavelengths ranging from approximately 256 to 584 A. A ratio of reflectivities for s- and p-polarized light, R(s):R(p) approximately , and a resolving power of lambda/Dlambda approximately 6 at 304 A were obtained. These characteristics and the use of a VYNS (a copolymer material composed of 90% vinyl chloride and 10% vinyl acetate) spectral filter were sufficient to allow a detailed polarization study of the first two members of the Lyman series of He(+) at wavelengths of 304 A (HeII p --> s) and 256 A (HeII p --> s) for impact-electron energies ranging from threshold to 1500 eV. The MLM has also been used as a single flat-surface mirror polarimeter for the analysis of longer-wavelength radiation (517 to 584 A) from the (snp) (1) P (o) --> (1s(2)) (1) S series of neutral He with R(s)/R(p) approximately. Although MLM polarimeters were previously used for EUV measurements with bright photon sources such as those provided by synchrotron facilities, the results presented clearly demonstrate the feasibility of such devices with lower-intensity electron and ion impact sources. The compact design of the apparatus makes it suitable as a portable measurement and calibration device.