Ultraintense Attosecond Pulse Emission from Relativistic Laser-Plasma Interaction

We develop an analytical model for ultraintense attosecond pulse emission in the highly relativistic laser-plasma interaction. In this model, the attosecond pulse is emitted by a strongly compressed electron layer around the instant when the layer transverse current changes the sign and its longitudinal velocity approaches the maximum. The emitted attosecond pulse has a broadband exponential spectrum and a stabilized constant spectral phase $\psi(\omega)=\pm\pi/2-\psi_{A_m}$. The waveform of the attosecond pulse is also given explicitly, to our knowledge, for the first time. We validate the analytical model via particle-in-cell (PIC) simulations for both normal and oblique incidence. Based on this model, we highlight the potential to generate an isolated ultraintense phase-stabilized attosecond pulseComment: 12 pages, 7 figure

Plasma High Harmonic Generation and Single Attosecond Pulse Emission from Ultraintense Laser Pulses

The thesis is devoted to the analytical and numerical studies of high-order harmonic generation and super-intense single attosecond pulse emission via ultra-relativistic laser-plasma interaction. In the ultra-relativistic regime, the laser radiation pressure induces plasma ion motion through the so called hole-boring effect, resulting in frequency widening of the harmonic spectra. This widening, analyzed analytically and validated by particle-in-cell simulations, produces a quasi-continuous frequency spectrum, a prerequisite for generating an intense single attosecond pulse. Based on the results and physical considerations, parameter maps highlighting the optimum regions for generating a single intense attosecond pulse and coherent XUV radiation are presented. Moreover, a robust plasma gating is developed to generate a super-intense phase-stabilized single attosecond pulse. The hole-boring effect limits the most efficient high-frequency emission in one laser cycle making it possible to isolate a single attosecond pulse. The generated pulse is characterized by a stabilized spectral phase ψ(ω) ≈ ±π/2 and an ultra-broad exponential spectrum up to keV region bounded by ROM scaling and CSE scaling. The unprecedented intensity highlights the potential of the isolated attosecond pulse for performing attosecond-pump attosecond-probe experiments

Interferences effects in polarized nonlinear Breit-Wheeler process

The creation of polarized electron-positron pairs by the nonlinear Breit-Wheeler process in short laser pulses is investigated using the Baier-Katkov semiclassical method beyond local-constant-field approximation (LCFA), which allows for identifying the interferences effects in the positron polarization. When the laser intensity is in the intermediate %multiphoton regime, the interferences of pair production in different formation lengths induce an enhancement of pair production probability for spin-down positrons, which significantly affects the polarization of created positrons. The polarization features are distinct from that obtained with LCFA, revealing the invalidity of LCFA in this regime. Meanwhile, the angular distribution for different spin states varies, resulting in an angular-dependent polarization of positrons. The average polarization of positrons at beam center is highly sensitive to the laser's carrier-envelope phase (CEP), which provides a potential alternative way of determining the CEP of strong lasers. The verification of the observed interference phenomenon is possible for the upcoming experiments