Laurence Kiernan

Extreme-ultraviolet studies with laser-produced plasmas

A new multilaser multichannel spectrometer system has been developed that allows a wide range of investigations of the interaction of extreme-ultraviolet (EUV) photons with matter in the form of free atoms or ions, e.g., in gases or plasmas or bound as in solids. The EUV photons are generated by a laser-produced plasma. Applications to the study of photoabsorption by thin foils, gases, and ground- and excited-state atoms and ions are described. The design and performance of a collimated, quasi-monochromatic, intense source of EUV radiation based on the combination of a laser-produced plasma with a EUV multilayer mirror is also reported.

High-resolution photoion yield measurements of 'hollow' atomic lithium

Using monochromatized extreme-UV radiation from the undulator beamline BW3 at HASYLAB we have measured at high resolution (E/ Delta E approximately 7000) the Li+ photoion yield spectrum at excitation energies corresponding to transitions to double K-shell vacancy states. A number of such resonances including single-photon-three-electron excitations, e.g. 1s22s(2S) to 2p3(2p), have been observed for the first time. The spectrum is tentatively classified with the aid of Hartree-Fock calculations.

2p-subshell photoabsorption by Si2+ ions in a laser-produced plasma

The 2p-subshell photoabsorption spectrum of Mg-like silicon has been recorded for the first time using the dual laser plasma (DLP) technique. The spectrum is discussed within a framework of the evolution of 2p photoabsorption along the Mg-like isoelectronic sequence. Assignments of the Si2+ spectrum based on Hartree-Fock configuration interaction (HFCI) calculations are presented.

The 2p-subshell photoabsorption spectrum of Al+ in a laser-produced plasma

The authors have recorded the time-resolved photoabsorption spectra of aluminium plasmas in the 50-200 AA wavelength range using the dual laser produced plasma technique (DLPP). Absorbing plasmas were generated by focusing the output from a pulsed dye or a Q-switched ruby laser onto an aluminium slab target. The continuum backlight was provided by irradiating a tantalum rod with the output from a time-synchronized Q-switched Nd-YAG laser. Some of the spectra were recorded with the aid of a toroidal mirror. By combining time and space resolution the authors have been able to isolate almost exclusively Al+ and record its photoabsorption spectrum. They provide an analysis of 2p to nd, (n+1)s Rydbergs in Al+ based on multiconfiguration ab initio atomic structure calculations and quantum defects for the higher members of each series. They have also observed and tentatively classified a number of members of the 2p63s2 to 2p53s3p2 doubly excited transition array.