M. H. R. Hutchinson

Broadly tunable vacuum-ultraviolet radiation source employing resonant enhanced sum–difference frequency mixing in krypton

Vacuum-ultraviolet (VUV) generation by resonant third-order sum–difference frequency conversion (wVUV = 2wR − wT) in krypton has been investigated. The frequency wR (λR = 212.55 nm) was resonant with the Kr two-photon transition 4p–5p[1/2, 0]. By tuning wT in the range λT = 220–860 nm it was possible to generate wVUV in the wavelength range λVUV = 200–120 nm. The conversion efficiency was enhanced in the range 121–123 nm by phase matching with a normally dispersive buffer gas (Ar); under the best phase-matched conditions employed, VUV output powers at the Lyman-α wavelength of the order of 1 kW were inferred from the estimated VUV pulse energy. This source was used to measure high-lying members of the Mg principal series near 162 nm. High resolution and excellent sensitivity of detection, when a thermionic diode detector was used, have been demonstrated.

Vulcan Petawatt—an ultra-high-intensity interaction facility

The Vulcan Nd : glass laser at the Central Laser Facility is a Petawatt (1015 W) interaction facility available to the UK and international user community. The facility came online to users in 2002 and considerable experience has been gained operating the Vulcan facility in this mode. The facility is designed to deliver irradiance on target of 1021 W cm−2 for a wide-ranging experimental programme in fundamental physics and advanced applications. This includes the interaction of super-high-intensity light with matter, fast ignition fusion research, photon induced nuclear reactions, electron and ion acceleration by light waves and the exploration of the exotic world of plasma physics dominated by relativity.

Explosion of atomic clusters heated by high-intensity femtosecond laser pulses

We have experimentally and theoretically studied the high-intensity ( .10 W cm), femtosecond photoionization of inertially confined noble-gas clusters. We have examined the energies of electrons and ions ejected during these interactions and found that particles with substantial kinetic energy are generated. Electrons with energies up to 3 keV and ions with energies of up to 1 MeV have been observed. These experimental observations are well explained by a theoretical model of the cluster as a small plasma sphere that explodes following rapid electron collisional heating by the intense laser pulse. @S1050-2947 ~97!02912-0#

INVESTIGATION OF HIGH-HARMONIC GENERATION FROM XENON ATOM CLUSTERS

We report on the generation of harmonic radiation (in the 70 - 90 nm range) from clusters of Xe atoms formed in a gas jet. We find that the harmonic yield from the clusters exhibits an anomalous cubic scaling with backing pressure to the gas jet. This scaling is consistent with a cluster dipole moment resulting from collective oscillations of electrons around the central ions of the cluster. Using a nanosecond ultraviolet prepulse to dissociate the clusters, we have also attempted to compare harmonic yields from clusters with those produced from monatomic Xe, under otherwise identical conditions. Our results suggest that yields from clusters might exceed those from monomers by up to a factor of five.

High-efficiency laser-pulse compression by stimulated Brillouin scattering.

Highly efficient compression of laser pulses down to 1 nsec in duration by stimulated Brillouin scattering has been demonstrated. Compression ratios of ~10 and energy-conversion efficiencies >70% have been produced. Several compressor systems have been investigated, including the use of tapered waveguides, long-focal-length geometries, and generator-amplifier systems.

Specular reflectivity of plasma mirrors as a function of intensity, pulse duration, and angle of incidence

The specular reflectivity of plasma mirrors formed by subpicosecond pulses from a titanium:sapphire laser has been measured for different angles of incidence and for two different pulse lengths as a function of the laser intensity. Laser pulses with energies up to 250 mJ and pulse durations of 90 and 500 fs were focused onto a fused silica substrate. For angles of incidence between 6° and 45° the specular reflectivity increases to values of about 80% for intensities above a certain threshold intensity. The threshold intensity varies with the pulse length but is nearly independent of the angle of incidence. For very high intensities the specular reflectivity drops again to values of only a few percent.

X-ray yields from Xe clusters heated by short pulse high intensity lasers

We have examined the absolute yield of keV x-rays emitted from gaseous plasmas created by the intense irradiation of large Xe clusters. We find that >10 μJ of x rays with photon energies above 1 keV are produced from clustering Xe gas targets when heated by 250 mJ, 2 ps laser pulses at an intensity of ∼1017 W/cm2. The yields show strong laser intensity dependence and variation with Xe cluster size.

Well characterized 1019W cm2 operation of VULCAN—an ultra-high power Nd:glass laser

Abstract Peak intensities of 1019 W cm2 have been reliably obtained from a high power Nd:glass laser using chirped pulse amplification. An Additive Pulse Modelocked oscillator incorporating diode pumped Nd:LMA was used to generate the sub-picosecond pulse. The focal spot intensity distribution has been characterized in detail showing a three times diffraction limited beam.

Integrated implosion/heating studies for advanced fast ignition

Integrated experiments to investigate the ultrafast heating of implosions using cone/shell geometries have been performed at the Rutherford Appleton Laboratory. The experiments used the 1054 nm, nanosecond, 0.9 kJ output of the VULCAN Nd:glass laser to drive 486 μm diameter, 6 μm wall thickness Cu-doped deuterated plastic (CD) shells in 6-beam cubic symmetry. Measurements of the opacity of the compressed plasma using two-dimensional spatially resolved Ti-Kα x-ray radiography suggest that densities of 4 g cm−3 and areal densities of 40 mg cm−2 were achieved at stagnation. Upper limits on the heating with both 1 ps and 10 ps pulses were deduced from the fluorescent yield from the Cu dopant. The data suggest that control of the preformed plasma scale-length inside the cone is necessary for efficient coupling to the compressed plasma.

keV x-ray spectroscopy of plasmas produced by the intense picosecond irradiation of a gas of xenon clusters

We have studied the characteristics of x-ray emission in the 12- range from plasmas produced by the irradiation of a target of Xe clusters with picosecond laser pulses at intensities near . These plasmas exhibit strong emission from Ni-like through to Mn-like Xe. We find that the strength and character of the x-ray spectra are very similar when either 1053 or 526 nm laser pulses are used to heat the clusters.