HARMONIC GENERATION IN REFLECTION FROM PLASMA MIRRORS

Abstract

The discovery of chirped-pulse amplification in 1985 has led to the development of powerful femtosecond lasers reaching the terawatt and petawatt levels. These lasers can produce intensities capable of ionizing any gas, liquid, or solid target, including the conventional optics that control ordinary light. This rapid increase in the intensity of lasers has prompted researchers to build plasma-based optics capable of handling light of ionizing intensities, including plasma mirrors, waveplates, q-plates, beam combiners and splitters, amplifiers, lenses, and gratings. The plasma mirror, in particular, has a broad range of applications, such as specular reflection and focusing, temporal and spatial cleaning, and generating harmonic orders of the driving laser's fundamental wavelength. This thesis presents experimental and computational modeling of intense lasers interacting with plasma mirrors, focusing on the emission of harmonics driven by lasers with tailored temporal waveforms and controlled polarization states. In addition to enabling harmonic generation with favorable temporal, spatial, and spectral properties, this work shows how manipulating light in all degrees of freedom allows for experimental control of relativistic plasma dynamics at the sub-optical-cycle timescale. Specifically, this thesis provides the first experimental demonstration of enhanced harmonic generation with a two-color laser compared to a single color alone from a multi-pass plasma mirror configuration. Additionally, a series of numerical studies using tailored light and structured plasmas is presented, revealing the emission of vortex harmonics in the specular and transmitted direction from a circularly polarized laser normally incident on an ultrathin plasma target, as well as an ellipticity-controlled harmonic source where the harmonic orders either co-rotate or counter-rotate with the reflected fundamental. Finally, this thesis identifies several numerical artifacts that arise when modeling high-density laser--solid interactions within the particle-in-cell framework, especially the appearance of single-cell density spikes that grow with increasing spatial resolution.