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A detailed investigation of excitation of He (1s2) 1S to He (1snp) 1P degree(s) (n equals 2 - 5) states and ionization-excitation of He (1s2) 1S to He (2p) 2P degree(s) and He (3p) 2P degree(s) states in e- + He and H+ + He collision systems is presented for a wide range of projectile velocities (2.2 a.u. < v < 6.9 a.u.). Specifically new experimental data are presented on measurements of the degree of linear polarization for excitation and excitation-ionization of He following proton impact in the extreme ultraviolet (EUV) wavelengths. These measurements have been performed using a characterized molybdenum/silicon multilayer mirror polarimeter (MLM) whose polarization characteristics have been optimized for EUV emission of He and He+. Furthermore, the proton experimental results are compared with theoretical polarization data using the first Born approximation and recent atomic orbital close coupling (AOCC) calculations for the excitation process. A comprehensive comparison of experimental data for negatively and positively charged projectiles at equal impact velocities is also given in order to elucidate differences in the collision mechanisms of two electron targets. It is important to note that these results are relevant for astrophysical diagnostics such as solar flares.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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 helium for wavelengths ranging from approximately 256 angstrom to 584 angstrom. A ratio of reflectivities for s and p polarized light, Rs/Rp approximately equals 10, and a resolving power of (lambda) /(Delta) (lambda) approximately equals 6 at 304 angstrom were obtained. These characteristics and the use of a VYNS26 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 angstrom (HeII 2p yields 1s) and 256 angstrom (HeII 3p yields 1s) 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 angstrom to 584 angstrom) from the HeI (1snp) 1Po yields (1s2) 1S series of neutral helium with Rs/Rp approximately equals 3. While MLM polarimeters have previously been used for EUV measurements with bright photon sources such as those provided by synchrotron facilities, the results from this work 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.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

New experimental results are presented on measurements of the degree of linear polarization for ionization-excitation of He following electron and proton impact on a He gas target. These measurements have been performed using an optically characterized molybdenum/silicon (Mo/Si) multilayer mirror (MLM) polarimeter whose reflection and polarization characteristics have been optimized for the 304 angstrom wavelength region. In particular, the polarization of the photon emission from the decay of HeII (2p) 2P0 yields (1s) 2S with a wavelength of 304 Angstrom (Lyman (alpha) of HeII) has been measured for electron impact energies ranging from threshold to 1500 eV. These results are compared with polarization measurements of HeII Lyman (alpha) following proton impact on He for 187 to 460 keV beam energy corresponding to 2.7 a.u. less than v less than 4.3 a.u. projectile velocities. The integral alignment parameter A0 is also provided for negatively and positively charged particle impact to elucidate similarities and differences in the collision dynamics of two electron targets such as helium. Such results are of importance for astrophysical and laboratory plasma diagnostics.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.