Photoionization Studies from Laser-Produced Plasmas to Synchrotron Radiation

Photoionization is used in many applications and research of atoms and molecules. Soft x-rays (SXR) are one particularly useful type of light employed in photoionization to analyze the structure of a molecule; but the main sources for SXRs, synchrotrons, are costly and not readily available. This work is part of the xLuminate project which aims to address the cost and availability constraints through the design, construction, and application of a laser-produced plasma (LPP) SXR source. Specifically, the presented work focuses on the application of SXRs through the construction of an electron-ion spectrometer and SXR photoionization experiments at the Elettra synchrotron, which provided experience with SXR applications. Additional work included improvements to a light-weight model for LPPs relevant to the xLuminate SXR source. The following work begins with the investigation of a staple collisional-radiative model for LPPs. The examination revealed the importance of ionization energies ($\ionEnergy$) to the model especially regarding the phenomenon of ionization bottlenecks at closed shell, stable electron configurations. With appropriate $\ionEnergy$ values, the electron orbital occupancy term was shown to be a quantum mechanical correction factor and unnecessary. A minor correction to the model was found and justified. Lastly, an upper temperature limit was established, and a path to compare the results of the model to experimental LPP spectra was demonstrated. Subsequent work encompassed the design of the electron-ion spectrometer. Velocity map imaging (VMI) was the technique chosen for the spectrometer, and a comparison of three VMI setups guided the design. Moreover, ion optics and particle flight trajectory simulations in the SIMION program highlighted that a variety of electrode voltages and positions can produce high quality VMI. SIMION simulations also explored the influence of an oven producing gaseous photoionization targets and demonstrated the oven can be used with an accountable and acceptable influence on the VMI quality. Both the comparison and the simulations lead to a final constructed versatile VMI spectrometer. Finally, research done at the GasPhase beamline of the Elettra Synchrotron, using a multi-coincidence angularly resolved electron spectrometer, is presented. The photodouble ionization (PDI) triple differential cross section (TDCS) was measured to bring further insight to resonant enhanced features in the PDI of aromatic hydrocarbons. Specifically, the PDI TDCS of thiophene (C4H4S) and benzene (C6H6) were measured for coincidence electrons under equal energy sharing conditions of 10 eV and 20 eV kinetic energy, since resonance enhancement is only expected for benzene at 20 eV. The lack of theoretical thiophene and benzene PDI models lead to a comparison with a multi-Gaussian model fit to the data. With a comparison to well known He PDI TDCS, the fit emphasized molecular differences and showed possible support for a distinct mechanism for the resonance enhancement.