| High intensity laser light was instrumental for notable advances across an exceptional range of disciplines including plasma physics, quantum control, attosecond science, molecular dynamics, inertial confinement fusion, and optical science. Current laser technology has brought about the next generation of ultra-high intensities (1019 W/cm2). Our common understanding of light-matter interactions breaks down at these extreme intensities, especially when the liberated photoelectron becomes relativistic and the effect of the laser magnetic field is no longer negligible. As the ultrastrong laser science frontier involves unprecedented energy scales from 1 keV to 1 MeV and opens up an abundance of new high energy atomic and molecular processes, photoionization dynamics of atoms and molecules in super- and ultra-high intensity fields become an area of interest. The work presented in this dissertation is carried out to provide a better answer to the fundamental question "How atoms and molecules interact with super- and ultra-intense light fields?" In particular, the presented work will cover quantitative measurements of ionization products, ions and photoelectrons, from strong- (1013 -- 1016 W/cm2) to ultra-strong (10 16 -- 1019 W/cm2) field ionization of noble gas atoms (Ne, Kr, and Xe) and hydrocarbon molecules (CH4).;In order to understand the molecular ionization processes at extreme intensities the ellipticity dependence of the ultrafast photoionization for Cn+ fragments from methane is investigated. The study extends from the strong field (C+, C2+) at 10 14 W/cm2 to the ultrastrong field (C5+) at 1018 W/cm2. The first precision measurements of ionization of Ne and Kr at 400 nm are presented from 1013 to 1017 W/cm2 for charge states up to Kr 8+. The findings indicate that ultraviolet to vacuum ultraviolet wavelengths can give the largest recollision for higher charge states. Experimental photoelectron measurements from single atom photoionization of noble gases exposed to field intensities up to 2 x 1019 W/cm2 are presented. Photoelectrons with energies of 1.4 MeV emitted into polar angles of 45° from the laser propagation vector were observed. Comparisons between neon, argon, and xenon reveal atomic structure, specifically electron shell binding energies, modifies the photoelectron energy spectra and highest energy cutoff. |
