Tailored laser pulse chirp to maintain optimum radiation pressure acceleration of ions

Ion beams generated with ultra-intense lasers-plasma accelerators hold promises to provide compact and affordable beams of relativistic ions. One of the most efficient acceleration setups was demonstrated to be direct acceleration by the laser's radiation pressure. Due to plasma instabilities developing in the ultra-thin foils required for radiation pressure acceleration, however, it is challenging to maintain stable acceleration over long distances. Recent studies demonstrated, on the other hand, that specially tailored laser pulses can shorten the required acceleration distance suppressing the onset of plasma instabilities. Here we extend the concept of specific laser pulse shapes to the experimentally accessible parameter of a frequency chirp. We present a novel analysis of how a laser pulse chirp may be used to drive a foil target constantly maintaining optimal radiation pressure acceleration conditions for in dependence on the target's areal density and the laser's local field strength. Our results indicate that an appropriately frequency chirped laser pulse yields a significantly enhanced acceleration to higher energies and over longer distances suppressing the onset of plasma instabilities.Comment: 7 pages, 4 figure

Time-dependent Kohn-Sham approach to quantum electrodynamics

We prove a generalization of the van Leeuwen theorem towards quantum electrodynamics, providing the formal foundations of a time-dependent Kohn-Sham construction for coupled quantized matter and electromagnetic fields. Thereby we circumvent the symmetry-causality problems associated with the action-functional approach to Kohn-Sham systems. We show that the effective external four-potential and four-current of the Kohn-Sham system are uniquely defined and that the effective four-current takes a very simple form. Further we rederive the Runge-Gross theorem for quantum electrodynamics.Comment: 8 page

Ultra-intense laser pulse characterization using ponderomotive electron scattering

We present a new analytical solution for the equation of motion of relativistic electrons in the focus of a high-intensity laser pulse. We approximate the electron's transverse dynamics in the averaged field of a long laser pulse focused to a Gaussian transverse profile. The resultant ponderomotive scattering is found to feature an upper boundary of the electrons' scattering angles, depending on the laser parameters and the electrons' initial state of motion. In particular, we demonstrate the angles into which the electrons are scattered by the laser scale as a simple relation of their initial energy to the laser's amplitude. We find two regimes to be distinguished in which either the laser's focusing or peak power are the main drivers of ponderomotive scattering. Based on this result, we demonstrate how the intensity of a laser pulse can be determined from a ring-shaped pattern in the spatial distribution of a high-energy electron beam scattered from the laser. We confirm our analysis by means of detailed relativistic test particle simulations of the electrons' averaged ponderomotive dynamics in the full electromagnetic fields of the focused laser pulse

Quantum anti-quenching of radiation from laser-driven structured plasma channels

We demonstrate that in the interaction of a high-power laser pulse with a structured solid-density plasma-channel, clear quantum signatures of stochastic radiation emission manifest, disclosing a novel avenue to studying the quantized nature of photon emission. In contrast to earlier findings we observe that the total radiated energy for very short interaction times, achieved by studying thin plasma channel targets, is significantly larger in a quantum radiation model as compared to a calculation including classical radiation reaction, i.e., we observe quantum anti-quenching. By means of a detailed analytical analysis and a refined test particle model, corroborated by a full kinetic plasma simulation, we demonstrate that this counter-intuitive behavior is due to the constant supply of energy to the setup through the driving laser. We comment on an experimental realization of the proposed setup, feasible at upcoming high-intensity laser facilities, since the required thin targets can be manufactured and the driving laser pulses provided with existing technology.Comment: 6 pages, 3 figure

Determining the carrier-envelope phase of intense few-cycle laser pulses

The electromagnetic radiation emitted by an ultra-relativistic accelerated electron is extremely sensitive to the precise shape of the field driving the electron. We show that the angular distribution of the photons emitted by an electron via multiphoton Compton scattering off an intense (I>10^{20}\;\text{W/cm^2}), few-cycle laser pulse provides a direct way of determining the carrier-envelope phase of the driving laser field. Our calculations take into account exactly the laser field, include relativistic and quantum effects and are in principle applicable to presently available and future foreseen ultra-strong laser facilities.Comment: 4 pages, 2 figure

Direct laser acceleration of electrons assisted by strong laser-driven azimuthal plasma magnetic fields.

A high-intensity laser beam propagating through a dense plasma drives a strong current that robustly sustains a strong quasistatic azimuthal magnetic field. The laser field efficiently accelerates electrons in such a field that confines the transverse motion and deflects the electrons in the forward direction. Its advantage is a threshold rather than resonant behavior, accelerating electrons to high energies for sufficiently strong laser-driven currents. We study the electron dynamics via a test-electron model, specifically deriving the corresponding critical current density. We confirm the model's predictions by numerical simulations, indicating energy gains two orders of magnitude higher than achievable without the magnetic field