489 research outputs found
Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering
Twisted Laguerre-Gaussian lasers, with orbital angular momentum and
characterised by doughnut shaped intensity profiles, provide a transformative
set of tools and research directions in a growing range of fields and
applications, from super-resolution microcopy and ultra-fast optical
communications to quantum computing and astrophysics. The impact of twisted
light is widening as recent numerical calculations provided solutions to
long-standing challenges in plasma-based acceleration by allowing for high
gradient positron acceleration. The production of ultrahigh intensity twisted
laser pulses could then also have a broad influence on relativistic
laser-matter interactions. Here we show theoretically and with ab-initio
three-dimensional particle-in-cell simulations, that stimulated Raman
backscattering can generate and amplify twisted lasers to Petawatt intensities
in plasmas. This work may open new research directions in non-linear optics and
high energy density science, compact plasma based accelerators and light
sources.Comment: 18 pages, 4 figures, 1 tabl
Weak collisionless shocks in laser-plasmas
We obtain a theory describing laminar shock-like structures in a collisionless plasma and examine the parameter limits, in terms of the ion sound Mach number and the electron/ion temperature ratio, within which these structures exist. The essential feature is the inclusion of finite ion temperature with the result that some ions are reflected from a potential ramp. This destroys the symmetry between upstream and downstream regions that would otherwise give the well-known ion solitary wave solution. We have shown earlier (Cairns et al 2014 Phys. Plasmas 21 022112) that such structures may be relevant to problems such as the existence of strong, localized electric fields observed in laser compressed pellets and laser acceleration of ions. Here we present results on the way in which these structures may produce species separation in fusion targets and suggest that it may be possible to use shock ion acceleration for fast ignition.PostprintPeer reviewe
Production of picosecond, kilojoule, petawatt laser pulses via Raman amplification of nanosecond pulses
Raman amplification in plasma has been promoted as a means of compressing
picosecond optical laser pulses to femtosecond duration to explore the
intensity frontier. Here we show for the first time that it can be used, with
equal success, to compress laser pulses from nanosecond to picosecond duration.
Simulations show up to 60% energy transfer from pump to probe pulses, implying
that multi-kiloJoule ultra-violet petawatt laser pulses can be produced using
this scheme. This has important consequences for the demonstration of
fast-ignition inertial confinement fusion.Comment: Minor revision to fix problem with image renderin
The effect of phase front deformation on the growth of the filamentation instability in laser–plasma interactions
Laser pulses of 0.9 kJ/1 ns/1053 nm were focused onto low-Z plastic targets in both spherical and planar geometry. The uniformity of the resulting plasma production was studied using x-ray pinhole imaging. Evidence is provided suggesting that thermal filamentation starts to occur for irradiances on the target of I lambda(2) >= 10(14) W cm(-2) mu m(2), even on deployment of phase plates to improve the focal spot spatial uniformity. The experiments are supported by both analytical modelling and two-dimensional particle-in-cell simulations. The implications for the applications of laser-plasma interactions that require high degrees of uniform irradiation are discussed
Measuring fast electron spectra and laser absorption in relativistic laser-solid interactions using differential bremsstrahlung photon detectors
A photon detector suitable for the measurement of bremsstrahlung spectra
generated in relativistically-intense laser-solid interactions is described.
The Monte Carlo techniques used to back-out the fast electron spectrum and
laser energy absorbed into fast electrons are detailed. A
relativistically-intense laser-solid experiment using frequency doubled laser
light is used to demonstrate the effective operation of the detector. The
experimental data was interpreted using the 3-spatial-dimension Monte Carlo
code MCNPX (Pelowitz 2008), and the fast electron temperature found to be 125
keV
Bright X-ray radiation from plasma bubbles in an evolving laser wakefield accelerator
We show that the properties of the electron beam and bright x-rays produced
by a laser wakefield accelerator can be predicted if the distance over which
the laser self-focuses and compresses prior to self-injection is taken into
account. A model based on oscillations of the beam inside a plasma bubble shows
that performance is optimised when the plasma length is matched to the laser
depletion length. With a 200~TW laser pulse this results in an x-ray beam with
median photon energy of \unit[20]{keV}, photons above
\unit[1]{keV} per shot and a peak brightness of \unit[3 \times
10^{22}]{photons~s^{-1}mrad^{-2}mm^{-2} (0.1\% BW)^{-1}}.Comment: 5 pages, 4 figure
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