Professor Simon Hooker

Abstract:

We present experiments and numerical simulations which demonstrate that fully-ionized, lowdensity plasma channels could be formed by hydrodynamic expansion of plasma columns produced by optical field ionization (OFI). Simulations of the hydrodynamic expansion of plasma columns formed in hydrogen by an axicon lens show the generation of 200 mm long plasma channels with axial densities of order ne(0) = 1 × 1017 cm−3 and lowest-order modes of spot size WM ≈ 40 µm. These simulations show that the laser energy required to generate the channels is modest: of order 1 mJ per centimetre of channel. The simulations are confirmed by experiments with a spherical lens which show the formation of short plasma channels with 1.5 × 1017 cm−3 . ne(0) . 1 × 1018 cm−3 and 61 µm & WM & 33 µm. Low-density plasma channels of this type would appear to be well-suited as multi-GeV laser-plasma accelerator stages capable of long-term operation at high pulse repetition rates.

Abstract:

© 2018 The Author(s). Discharge capillary-based active plasma lenses are a promising new technology for strongly focusing charged particle beams, especially when combined with novel high gradient acceleration methods. Still, many questions remain concerning such lenses, including their transverse field uniformity, limitations due to plasma wakefields and whether they can be combined in multi-lens lattices in a way to cancel chromaticity. These questions will be addressed in a new plasma lens experiment at the CLEAR User Facility at CERN. All the subsystems have been constructed, tested and integrated into the CLEAR beam line, and are ready for experiments starting late 2017.

Abstract:

High harmonic generation (HHG) is a promising tabletop source of coherent short wavelength radiation, with applications spanning science and engineering [1]. However, the low conversion efficiency and low average power of conventional few-kHz near-infrared (NIR) driving lasers limits the photon flux of such sources. Scaling this technique to MHz driving lasers requires strong focusing due to the limited pulse energy, and as a result the interaction volume is greatly reduced. It has been shown that this may be mitigated by restricting HHG to a photonic crystal fiber (PCF) [2, 3]. Here, we explore HHG in the latest generation of negative curvature PCFs [4] and achieve the highest photon energies to date.