Phys Rev Lett 104 (2010) 225001-
By use of high intensity XUV radiation from the FLASH free-electron laser at DESY, we have created highly excited exotic states of matter in solid-density aluminum samples. The XUV intensity is sufficiently high to excite an inner-shell electron from a large fraction of the atoms in the focal region. We show that soft-x-ray emission spectroscopy measurements reveal the electronic temperature and density of this highly excited system immediately after the excitation pulse, with detailed calculations of the electronic structure, based on finite-temperature density functional theory, in good agreement with the experimental results.
REVIEW OF SCIENTIFIC INSTRUMENTS 81 (2010)
Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)
We present the progress made in developing IOPW OPCPA facility for the Vulcan laser to produce pulses with focused intensities >1023 Wcm-2. This power level will be delivered by generating pulses with >300J in 30fs. These pulses will be delivered to two target areas: in one target area they will be combined with the existing Vulcan Petawatt beamline and a new target area will be created for high intensity interactions. © 2010 Optical Society of America.
Experimental detection of post-soliton structures following high intensity laser interaction with a sub-critical gas jet
37th EPS Conference on Plasma Physics 2010, EPS 2010 3 (2010) 1960-1963
Measurement of fast electrons spectra generated by interaction between solid target and peta watt laser
Journal of Physics: Conference Series 244 (2010)
Fast electron energy spectra have been measured for a range of intensities between 1018 Wcm-2 and 1021 Wcm-2 and for different target materials using electron spectrometers. Several experimental campaigns were conducted on peta watt laser facilities at the Rutherford Appleton Laboratory and Osaka University. In these experimental campaigns, the pulse duration was varied from 0.5 ps to 5 ps. The laser incident angle was also changed from normal incidence to 40° in p-polarized. The results show a reduction from the ponderomotive scaling on fast electrons over 1020 Wcm-2. © 2010 IOP Publishing Ltd.
Journal of Physics: Conference Series 244 (2010)
Collimated transport of fast electron beam through solid density matter is one of the key issues behind the success of the fast ignition scheme by means of which the required amount of ignition energy can be delivered to the hot spot region of the compressed fuel. Here we report on a hot electron beam collimation scheme in solids by tactfully using the strong magnetic fields generated by an electrical resistivity gradient according to Faraday's law. This was accomplished by appropriately fabricating the targets in such a way that the electron beam is directed to flow in a metal which is embedded in a much lower resistivity and atomic number metal. Experimental results showed guided transport of hot electron beam over hundreds of microns length inside solid density plasma, which were obtained from two experiments examining the scheme for petawatt laser driven hot electron beam while employing various target configurations. © 2010 IOP Publishing Ltd.
Soft X-ray scattering using FEL radiation for probing near-solid density plasmas at few electron volt temperatures
High Energy Density Physics 6 (2010) 15-20
We report on soft X-ray scattering experiments on cryogenic hydrogen and simple metal samples. As a source of intense, ultrashort soft X-ray pulses we have used free-electron laser radiation at 92 eV photon energy from FLASH at DESY, Hamburg. X-ray pulses with energies up to 150 μJ and durations 15-50 fs provide interaction with the sample leading simultaneously to plasma formation and scattering. Experiments exploiting both of these interactions have been carried out, using the same experimental setup. Firstly, recording of soft X-ray inelastic scattering from near-solid density hydrogen plasmas at few electron volt temperatures confirms the feasibility of this diagnostics technique. Secondly, the soft X-ray excitation of few electron volt solid-density plasmas in bulk metal samples could be studied by recording soft X-ray line and continuum emission integrated over emission times from fs to ns. © 2009 Elsevier B.V.
Inferring the electron temperature and density of shocked liquid deuterium using inelastic X-ray scattering
Journal of Physics: Conference Series 244 (2010)
An experiment designed to launch laser-ablation-driven shock waves (10 to 70 Mbar) in a planar liquid-deuterium target on the OMEGA Laser System and to diagnose the shocked conditions using inelastic x-ray scattering is described. The electron temperature (T ) is inferred from the Doppler-broadened Compton-downshifted peak of the noncollective (α = 1kλ > 1) x-ray scattering for T > T . The electron density (n ) is inferred from the downshifted plasmon peak of the collective (α > 1) x-ray scattering. A cylindrical layer of liquid deuterium is formed in a cryogenic cell with 8-μm-thick polyimide windows. The polyimide ablator is irradiated with peak intensities in the range of 10 to 10 W/cm and shock waves are launched. Predictions from a 1-D hydrodynamics code show the shocked deuterium has a thickness of ∼0.1 mm with spatially uniform conditions. For the drive intensities under consideration, electron density up to ∼5 × 10 cm and electron temperature in the range of 10 to 25 eV are predicted. A laser-irradiated saran foil produces Cl Ly emission. The spectrally resolved x-ray scattering is recorded at 90° for the noncollective scattering and at 40° for the collective scattering with a highly oriented pyrolytic graphite (HOPG) crystal spectrometer and an x-ray framing camera. © 2010 IOP Publishing Ltd.
High Energy Density Physics 6 (2010) 109-112
The FLASH XUV-free electron laser has been used to irradiate solid samples at intensities of the order 1016 W cm-2 at a wavelength of 13.5 nm. The subsequent time integrated XUV emission was observed with a grating spectrometer. The electron temperature inferred from plasma line ratios was in the range 5-8 eV with electron density in the range 1021-1022 cm-3. These results are consistent with the saturation of absorption through bleaching of the L-edge by intense photo-absorption reported in an earlier publication. © 2009 Elsevier B.V. All rights reserved.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 81 (2010)
We employ a pseudopotential approach to investigate the screening of ionic cores in partially ionized plasmas. Here, the effect of the tightly bound electrons is condensed into an effective potential between the (free) valence electrons and the ionic cores. Even for weak electron-ion coupling, the corresponding screening clouds show strong modifications from the Debye result for elements heavier than helium. Modifications of the theoretically predicted x-ray scattering signal and implications on measurements are discussed. © 2010 The American Physical Society.
REVIEW OF SCIENTIFIC INSTRUMENTS 80 (2009) ARTN 083501
Physics of Plasmas 16 (2009)
Fast electron energy spectra have been measured for a range of intensities between 10 and 10 W cm-2 and for different target materials using electron spectrometers. Several experimental campaigns were conducted on petawatt laser facilities at the Rutherford Appleton Laboratory and Osaka University, where the pulse duration was varied from 0.5 to 5 ps relevant to upcoming fast ignition integral experiments. The incident angle was also changed from normal incidence to 40° in p -polarized. The results confirm a reduction from the ponderomotive potential energy on fast electrons at the higher intensities under the wide range of different irradiation conditions. © 2009 American Institute of Physics.
Physics of Plasmas 16 (2009) 112702-112702
Nail-wire targets (20 μm diameter copper wires with 80 μm hemispherical head) were used to investigate energy transport by relativistic fast electrons generated in intense laser-plasma interactions. The targets were irradiated using the 300 J, 1 ps, and 2 × 10 W · cm Vulcan laser at the Rutherford Appleton Laboratory. A spherically bent crystal imager, a highly ordered pyrolytic graphite spectrometer, and single photon counting charge-coupled device gave absolute Cu Kα measurements. Results show a concentration of energy deposition in the head and an approximately exponential fall-off along the wire with about 60 μm 1/e decay length due to resistive inhibition. The coupling efficiency to the wire was 3.3 ± 1.7% with an average hot electron temperature of 620 ± 125 keV. Extreme ultraviolet images (68 and 256 eV) indicate additional heating of a thin surface layer of the wire. Modeling using the hybrid E-PLAS code has been compared with the experimental data, showing evidence of resistive heating, magnetic trapping, and surface transport. © 2009 American Institute of Physics.
Evidence of anomalous resistivity for hot electron propagation through a dense fusion core in fast ignition experiments
New Journal of Physics 11 (2009)
Anomalous resistivity for hot electrons passing through a dense core plasma is studied for fast ignition laser fusion. The hot electrons generated via the ultra-intense laser pulse and guiding cone interactions are measured after they pass through a dense plasma with a density of 50-100 g cm-3 in a radius of 15-25 m. When significant neutron enhancements are achieved by the ultraintense laser pulse injection, the energy reduction of fast electrons is observed. Also, a reduction in the number of electrons with energy up to 15 MeV can be seen. We offer a new physical mechanism for the stopping of electrons, involving electron magnetohydrodynamic shock formation in the inhomogeneous plasma density region. The dissipation in the shock region can explain electron stopping with energies of the order of 15 MeV. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Temperature profiles derived from transverse optical shadowgraphy in ultraintense laser plasma interactions at 6 × 10 W cm?
Physics of Plasmas 16 (2009)
A variety of targets with different dimensions and materials was irradiated using the VULCAN PW laser [C. N. Danson, Nucl. Fusion 44, S239 (2004)]. Using transverse optical shadowgraphy in conjunction with a one-dimensional radiation hydrodynamics code it was possible to determine a longitudinal temperature gradient. It was demonstrated for thick targets with a low Z substrate and a thin higher Z tracer layer at the rear that the boundary between the two materials was Rayleigh-Taylor unstable. By including a simple bubble growth model into the calculations it was possible to correct for the associated behavior with regard to temperature. The resulting temperature gradient was in good agreement with the previously published data using two different methods of determining the temperature. © 2009 American Institute of Physics.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 80 (2009)
We have studied the dynamics of warm dense Li with near-elastic x-ray scattering. Li foils were heated and compressed using shock waves driven by 4-ns-long laser pulses. Separate 1-ns-long laser pulses were used to generate a bright source of 2.96 keV Cl Ly- α photons for x-ray scattering, and the spectrum of scattered photons was recorded at a scattering angle of 120° using a highly oriented pyrolytic graphite crystal operated in the von Hamos geometry. A variable delay between the heater and backlighter laser beams measured the scattering time evolution. Comparison with radiation-hydrodynamics simulations shows that the plasma is highly coupled during the first several nanoseconds, then relaxes to a moderate coupling state at later times. Near-elastic scattering amplitudes have been successfully simulated using the screened one-component plasma model. Our main finding is that the near-elastic scattering amplitudes are quite sensitive to the mean ionization state Z̄ and by extension to the choice of ionization model in the radiation- hydrodynamics simulations used to predict plasma properties within the shocked Li. © 2009 The American Physical Society.
IEEE International Conference on Plasma Science (2009)
Plasma Physics and Controlled Fusion 51 (2009)
High Energy Density Physics 5 (2009) 212-215
We have performed measurements of the radiation and the hot electron temperature in sub-millimetre size hohlraums driven by a high intensity short-pulse laser. The results indicate that radiation temperatures ∼80 eV can be obtained with ∼20 J of laser energy delivered on target. Radiation-hydrodynamics simulations indicate an absorption into thermal X-rays of ≲1-2%, with peak temperatures similar to those measured experimentally. Crown Copyright © 2009.
Optics InfoBase Conference Papers (2009)
The temporal resolution of existing streak cameras are limited by electron transit time dispersion. Here we present a state-of-art design compensating this to achieve a breakthrough of 100fs time resolution. © 2009 OSA/CLEO/IQEC 2009.