High harmonic generation (HHG) by intense femtosecond laser pulses has, over the last three decades, provided new coherent sources of extreme ultraviolet and soft x-ray light and enabled the field of attosecond science. Furthermore, as properties of the target are encoded in the harmonic emission, high harmonic spectroscopy has allowed extraction of molecular structure and dynamics from the spectra and polarization states of harmonics generated from gas-phase molecules. HHG from solids, discovered in 2011, now promises to offer similar benefits to condensed matter physics. In this dissertation, I describe progress on two fronts: extending attosecond techniques to generate new high harmonic sources based on solid-state targets, and applying high harmonic spectroscopy to probe symmetry properties of solids. First, I demonstrate HHG from ZnO crystals using a high-power source of femtosecond mid-infrared pulses, and characterize the dependence of the harmonic spectrum on the orientation of the crystal with respect to the laser polarization. New features are observed in the orientation-dependent spectrum, which can be explained using symmetries associated with the transition dipoles. The same features are then investigated through polarization-resolved measurements of even and odd harmonic orders, which suggest a universal polarization behavior that is dictated largely by symmetry properties of the target. To test this conclusion, I investigate HHG from ferroelectric BaTiO3 and LiNbO3 crystals, for which the symmetry properties can be externally controlled. Due to their unique temporal resolution, high harmonic pulses are capable of probing rapidly occurring phenomena such as carrier interactions and phase transition dynamics. For this reason, it is desirable to develop harmonic sources with few-femtosecond to attosecond pulse durations. I take advantage of nonlinear compression in a bulk crystal to compress the mid-infrared laser pulse to < 3 optical cycles. Employing these pulses for HHG may pave the way toward novel compact, high-power attosecond sources.
Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Gholam Mirzaeimoghadar, Shima, "Symmetry and High Harmonic Spectroscopy in Solids" (2020). Electronic Theses and Dissertations, 2020-. 438.