Relativistic interaction of ultra-short laser pulses with nanostructured solids

Generation of hot and dense plasmas under relativistic interaction of ultra-intense high-contrast femtosecond laser pulses with solid targets is among the most exciting research topics in high energy density physics. Such plasmas would be also extremely beneficial for the area of astrophysics and nuclear physics, for the development of the efficient sources of hard-X-ray radiation. Nanophotonics opens a new chapter in this research. It was recently argued that nanowire arrays used as targets allow a larger penetration depth of the laser energy to a m-scale leading to the volumetric plasma heating. As a result of the very efficient laser energy absorption, electron densities of 1023-1024 cm-3 with multi-keV temperatures can be reached. However, this relatively new field research is still poorly understood, while no thorough comparative studies of the interaction with flat and nanostructured solids have been conducted. This thesis investigates the influence of the target morphology on the plasma parameters and produced hard X-ray emission in different regimes of interaction. The potential of the nanowires has been studied in a number of experiments with a focus on X-ray spectroscopy techniques. Besides the commonly used approach utilizing short-wavelength laser pulses (UV, visible or near-IR spectral range) for the production of laser-induced plasmas, a novel regime of interaction with long-wavelength pulses (mid-IR) has been investigated. The performed analysis of the measured X-ray spectra together with the Particle-In-Cell code and FLYCHK (collisional radiative code) simulations have shown that the plasma dynamics in the case of the nanowire and flat targets are strikingly different. This results in the effective heating of the plasma volume. It has been demonstrated that the nanowire morphology provides a possibility to generate a larger volume of hot dense plasmas at the given laser pulse parameters

Measurements of fluence profiles in femtosecond laser sparks and superfilaments in air

We investigate the nonlinear propagation of multiterawatt femtosecond laser pulses at 800 nm wavelength in air, under different external focusing conditions. We profile the laser beam in the vicinity of the nonlinear focus using a technique based on the dependence of the single-shot ablation threshold for gold on the angle of incidence of the laser beam on the sample. Under very tight focusing conditions (f number similar to 15) we observe the propagation regime reminiscent of the nanosecond optical breakdown. No clear individual filaments are formed across the beam, and the estimated peak intensity surges to at least 200 TW/cm(2). As the external focusing is loosened to f number similar to 125, we observe the transition to the multifilamentation regime. Distinct individual filaments are formed before the linear focus while the peak intensity reaches similar to 80 TW/cm(2). Once formed, the filaments do not coalesce into a single or few superfilaments as they pass through the focus zone. Our experimental observations are supported by numerical simulations.U.S. Air Force Office of Scientific Research under MURI [FA9550-16-1-0013]; Laserlab-Europe Project [HIJ-FSU002344]; Friedrich-Schiller-Universitat Jena; University of ArizonaThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]