Single-Shot Diagnosis of Electron Energy Evolution via Streaked Betatron X Rays in a Curved Laser Wakefield Accelerator.

We report on an experimental observation of the streaking of betatron x rays in a curved laser wakefield accelerator. The streaking of the betatron x rays was realized by launching a laser pulse into a plasma with a transverse density gradient. By controlling the plasma density and the density gradient, we realized the steering of the laser driver, electron beam, and betatron x rays simultaneously.

Shot-to-shot electron beam pointing instability in a nonlinear plasma bubble.

Shot-to-shot electron beam pointing instability in the plasma bubble, defined here as electron beam pointing jitter (EBJ), is a long-standing problem that limits the potential of the laser wakefield accelerator (LWFA) in a range of demanding applications. In general, EBJ is caused by variations in laser and plasma parameters from shot to shot, although the exact physical mechanism by which EBJ grows in the plasma wave remains unclear. In this work we theoretically investigate the fundamental physics of EBJ inside the plasma bubble and show how the intrinsic betatron oscillation can act as an amplifier to enhance EBJ growth.

Accelerating Ions by Crossing Two Ultraintense Lasers in a Near-Critical Relativistically Transparent Plasma.

A new scheme of ion acceleration by crossing two ultraintense laser pulses in a near-critical relativistically transparent plasma is proposed. One laser, acting as a trigger, preaccelerates background ions in its radial direction via the laser-driven shock. Another crossed laser drives a comoving snowplow field which traps some of the preaccelerated ions and then efficiently accelerates them to high energies up to a few giga-electron-volts.

Polarization-Dependent Self-Injection by Above Threshold Ionization Heating in a Laser Wakefield Accelerator.

We report on the experimental observation of a decreased self-injection threshold by using laser pulses with circular polarization in laser wakefield acceleration experiments in a nonpreformed plasma, compared to the usually employed linear polarization. A significantly higher electron beam charge was also observed for circular polarization compared to linear polarization over a wide range of parameters. Theoretical analysis and quasi-3D particle-in-cell simulations reveal that the self-injection and hence the laser wakefield acceleration is polarization dependent and indicate a different injection mechanism for circularly polarized laser pulses, originating from larger momentum gain by electrons during above threshold ionization.

Optimizing Laser Pulses for Narrow-Band Inverse Compton Sources in the High-Intensity Regime.

Scattering of ultraintense short laser pulses off relativistic electrons allows one to generate a large number of X- or gamma-ray photons with the expense of the spectral width-temporal pulsing of the laser inevitable leads to considerable spectral broadening. In this Letter, we describe a simple method to generate optimized laser pulses that compensate the nonlinear spectrum broadening and can be thought of as a superposition of two oppositely linearly chirped pulses delayed with respect to each other. We develop a simple analytical model that allows us to predict the optimal parameters of such a two-pulse-the delay, amount of chirp, and relative phase-for generation of a narrow-band γ-ray spectrum.