M. Spinks

Quasi-monoenergetic laser-plasma acceleration of electrons to 2 GeV

Laser-plasma accelerators of only a centimetre’s length have produced nearly monoenergetic electron bunches with energy as high as 1 GeV. Scaling these compact accelerators to multi-gigaelectronvolt energy would open the prospect of building X-ray free-electron lasers and linear colliders hundreds of times smaller than conventional facilities, but the 1 GeV barrier has so far proven insurmountable. Here, by applying new petawatt laser technology, we produce electron bunches with a spectrum prominently peaked at 2 GeV with only a few per cent energy spread and unprecedented sub-milliradian divergence. Petawatt pulses inject ambient plasma electrons into the laser-driven accelerator at much lower density than was previously possible, thereby overcoming the principal physical barriers to multi-gigaelectronvolt acceleration: dephasing between laser-driven wake and accelerating electrons and laser pulse erosion. Simulations indicate that with improvements in the laser-pulse focus quality, acceleration to nearly 10 GeV should be possible with the available pulse energy.

Impact of pre-plasma on fast electron generation and transport from short pulse, high intensity lasers

Previous experiments and modeling examining the impact of an underdense, pre-formed plasma in laser-plasma interactions have shown that the fast electrons are generated with energies higher than predicted by ponderomotive scaling [4, 3–14]. We report on experiments using the Texas Petawatt high intensity (150 fs, 1.5 × 1020 W cm−2) laser pulse, which were conducted to examine the mechanism for accelerating these high energy electrons. These experiments gauge the impact a controlled low density pre-formed plasma has on electron generation with a shorter time scale than previous experiments, 150–180 fs. Electron temperatures measured via magnetic spectrometer on experiment were found to be independent of preformed plasma. Supplemental computational results using 1D PIC simulations predict that super-ponderomotive electrons are generated inside a potential well in the pre-plasma [1]. However, while the potential well is established around 150 fs, the electrons require at least an additional 50 fs to be trapped and heated inside it.

Full-aperture backscatter diagnostics and applications at the Texas Petawatt Laser facility

In this paper, we present the development and application of a full-aperture backscatter diagnostics system at the Texas Petawatt Laser (TPW) facility. The diagnostic system includes three independent diagnostic stations. With this system, we obtained TPW on-shot focus properties, and high-harmonic spectral emission from solid foils (e.g., Cu and Al) and their Si substrate in an experiment to study laser hole boring, which show the hole-boring mechanism at relativistic intensities. The measured on-target full-power focal spots from ultrathin film targets help determine the optimum target thickness at certain laser contrast parameters for particle acceleration and neutron generation experiment, which is also a relative measurement of shot-toshot intensity fluctuations.

Pulse Contrast Measurements of the Texas Petawatt Laser

Temporal contrast of the Texas Petawatt laser is presented. The contrast is influenced by pencil beam prepulses on the timescale up to 110ns and by parametric fluorescence on the timescale of the OPCPA pump laser.

The Texas petawatt laser and current experiments

The Texas Petawatt Laser is operational with experimental campaigns executed in both F/40 and F3 target chambers. Recent improvements have resulted in intensities of >2×1021 W/cm2 on target. Experimental highlights include, accelerated electron energies of >2 GeV, DD fusion ion temperatures >25 keV and isochorically heated solids to 10-50 eV.

Generation of dark-current-free quasi-monoenergetic 1.25 GeV electrons by laser wakefield acceleration

We report electron acceleration to 1.25 GeV by petawatt-laser-driven wakefield acceleration at plasma density 5×1017 cm3. Electron beams are dark-current-free, quasi-monoenergetic, highly collimated (<;1mrad divergence), contain tens of pC and have excellent pointing stability.

Betatron x-rays from GeV laser-plasma-accelerated electrons

X-rays are produced when laser-wakefield accelerated electrons oscillate in the transverse electrostatic field of the accelerating structure. The measured characteristics of these betatron x-rays follow scaling laws relating them to the electron energy, charge, plasma density, and other observables. Here we report on the x-rays produced by electrons accelerated to energies >1 GeV and investigate the scaling laws for photon number, critical energy, and beam divergence.

GeV Electrons and High brightness Betatron X-rays from Petawatt-Laser-Driven Plasma Accelerators

We identify three regimes of correlated GeV-electron/keV-betatron-X-ray generation by a laser-plasma accelerator driven by the Texas Petawatt laser, and relate them to variations in strength of blowout, injection geometry and beam loading.

Lessons on Ultrahigh Peak Power Laser Performance from the Texas PetawattLaser

With a low repetition rate petawatt-class laser system, effective data collection requires repeatable laser performance, and even more importantly experimenters need to accurately know the parameters of each laser pulse. The presentation describes challenges of measuring ultrahigh peak power laser pulse parameters, how we address them, and the performance variance achieved on the Texas Petawatt Laser. Pulse duration, profile, spectrum, and energy, plus system prepulse contrast are discussed. Article not available.