Multi-GeV Electron Acceleration in Wakefields Strongly Driven by Oversized Laser Spots.

Experiments were performed on laser wakefield acceleration in the highly nonlinear regime. With laser powers P<250  TW and using an initial spot size larger than the matched spot size for guiding, we were able to accelerate electrons to energies E_{max}>2.5  GeV, in fields exceeding 500  GV m^{-1}, with more than 80 pC of charge at energies E>1  GeV.

A laser wakefield acceleration facility using SG-II petawatt laser system.

Laser wakefield acceleration (LWFA) using PW-class laser pulses generally requires cm-scale laser-plasma interaction Rayleigh length, which can be realized by focusing such pulses inside a long underdense plasma with a large f-number focusing optic. Here, we present a new PW-based LWFA instrument at the SG-II 5 PW laser facility, which employs f/23 focusing. The setup also adapted an online probing of the plasma density via Nomarski interferometry using a probe laser beam having 30 fs pulse duration.

Sliding-wave acceleration of ions in high-density gas jet targets.

A hybrid mechanism of ion acceleration is investigated which demonstrates the higher spectral density of protons at high energies. The interaction of few-cycle terrawatt laser pulses with near-critical density gas target is studied with the help of two-dimensional particle-in-cell simulation. The generation of few MeV protons with high spectral concentration near cutoff is attributed to the propagation of solitary waves in the decaying density profile of the gas jet.

Characterisation and Modelling of Ultrashort Laser-Driven Electromagnetic Pulses.

Recent advances on laser technology have enabled the generation of ultrashort (fs) high power (PW) laser systems. For such large scale laser facilities there is an imperative demand for high repetition rate operation in symbiosis with beamlines or end-stations. In such extreme conditions the generation of electromagnetic pulses (EMP) during high intense laser target interaction experiments can tip the scale for the good outcome of the campaign.

A laser-plasma accelerator driven by two-color relativistic femtosecond laser pulses.

A typical laser-plasma accelerator (LPA) is driven by a single, ultrarelativistic laser pulse from terawatt- or petawatt-class lasers. Recently, there has been some theoretical work on the use of copropagating two-color laser pulses (CTLP) for LPA research. Here, we demonstrate the first LPA driven by CTLP where we observed substantial electron energy enhancements.

High energy proton micro-bunches from a laser plasma accelerator.

Recent advances on laser-driven ion accelerators have sparked an increased interest in such energetic particle sources, particularly towards the viability of their usage in a breadth of applications, such as high energy physics and medical applications. Here, we identify a new ion acceleration mechanism and we demonstrate, via particle-in-cell simulations, for the first time the generation of high energy, monochromatic proton micro-bunches while witnessing the acceleration and self-modulation of the accelerated proton beam in a dual-gas target, consisting of mixed ion species. In the proposed ion acceleration mechanism due to the interaction of an ultra-short, ultra-intense (2 PW, 20 fs) laser pulses with near-critical-density partially ionized plasmas (C & H species), we numerically observed high energy monochromatic proton microbunches of high quality (peak proton energy 350 MeV, laser to proton conversion efficiency ~10 and angular divergence <10 degree), which can be of high relevance for medical applications.

High-resolution μCT of a mouse embryo using a compact laser-driven X-ray betatron source.

In the field of X-ray microcomputed tomography (μCT) there is a growing need to reduce acquisition times at high spatial resolution (approximate micrometers) to facilitate in vivo and high-throughput operations. The state of the art represented by synchrotron light sources is not practical for certain applications, and therefore the development of high-brightness laboratory-scale sources is crucial. We present here imaging of a fixed embryonic mouse sample using a compact laser-plasma-based X-ray light source and compare the results to images obtained using a commercial X-ray μCT scanner.

Coherent control of high harmonic generation via dual-gas multijet arrays.

High harmonic generation (HHG) is a central driver of the rapidly growing field of ultrafast science. We present a novel quasiphase-matching (QPM) concept with a dual-gas multijet target leading, for the first time, to remarkable phase control between multiple HHG sources (>2) within the Rayleigh range. The alternating jet structure with driving and matching zones shows perfect coherent buildup for up to six QPM periods.

Complete temporal characterization of asymmetric pulse compression in a laser wakefield.

We present complete experimental characterization of the temporal shape of an intense ultrashort 200-TW laser pulse driving a laser wakefield. The phase of the pulse was uniquely measured by using (second-order) frequency-resolved optical gating. The pulses are asymmetrically compressed and exhibit a positive chirp consistent with the expected asymmetric self-phase-modulation due to photon acceleration or deceleration in a relativistic plasma wave.

Fast advection of magnetic fields by hot electrons.

Experiments where a laser-generated proton beam is used to probe the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target are presented. At intensities of 10(15)   W  cm(-2) and under conditions of significant fast electron production and strong heat fluxes, the electron mean-free-path is long compared with the temperature gradient scale length and hence nonlocal transport is important for the dynamics of the magnetic field in the plasma. The hot electron flux transports self-generated magnetic fields away from the focal region through the Nernst effect [A.

Characterization of high-intensity laser propagation in the relativistic transparent regime through measurements of energetic proton beams.

Experiments were performed to investigate the propagation of a high intensity (I approximately 10(21) W cm(-2)) laser in foam targets with densities ranging from 0.9n(c) to 30n(c). Proton acceleration was used to diagnose the interaction.

Monoenergetic electronic beam production using dual collinear laser pulses.

The production of monoenergetic electron beams by two copropagating ultrashort laser pulses is investigated both by experiment and using particle-in-cell simulations. By proper timing between guiding and driver pulses, a high-amplitude plasma wave is generated and sustained for longer than is possible with either of the laser pulses individually, due to plasma waveguiding of the driver by the guiding pulse. The growth of the plasma wave is inferred by the measurement of monoenergetic electron beams with low divergence that are not measured by using either of the pulses individually.

Laser-driven acceleration of electrons in a partially ionized plasma channel.

The generation of quasimonoenergetic electron beams, with energies up to 200 MeV, by a laser-plasma accelerator driven in a hydrogen-filled capillary discharge waveguide is investigated. Injection and acceleration of electrons is found to depend sensitively on the delay between the onset of the discharge current and the arrival of the laser pulse. A comparison of spectroscopic and interferometric measurements suggests that injection is assisted by laser ionization of atoms or ions within the channel.

Effect of laser-focusing conditions on propagation and monoenergetic electron production in laser-wakefield accelerators.

The effect of laser-focusing conditions on the evolution of relativistic plasma waves in laser-wakefield accelerators is studied both experimentally and with particle-in-cell simulations. For short focal-length (w_{0} View Article and Find Full Text PDF

Magnetic reconnection and plasma dynamics in two-beam laser-solid interactions.

We present measurements of a magnetic reconnection in a plasma created by two laser beams (1 ns pulse duration, 1 x 10(15) W cm(-2)) focused in close proximity on a planar solid target. Simultaneous optical probing and proton grid deflectometry reveal two high velocity, collimated outflowing jets and 0.7-1.