P. LalousisInstitute of Electronic Structure and Lasers FORTH
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Measured highly elevated gains of proton–boron (HB11) fusion (Picciotto et al., Phys. Rev. X 4, 031030 (2014)) confirmed the exceptional avalanche reaction process (Lalousis et al., Laser Part. Beams 32, 409 (2014); Hora et al., Laser Part. Beams 33, 607 (2015)) for the combination of the non-thermal block ignition using ultrahigh intensity laser pulses of picoseconds duration. The ultrahigh acceleration above 1020 cm s??2 for plasma blocks was theoretically and numerically predicted since 1978 (Hora, Physics of Laser Driven Plasmas (Wiley, 1981), pp. 178 and 179) and measured (Sauerbrey, Phys. Plasmas 3, 4712 (1996)) in exact agreement (Hora et al., Phys. Plasmas 14, 072701 (2007)) when the dominating force was overcoming thermal processes. This is based on Maxwell’s stress tensor by the dielectric properties of plasma leading to the nonlinear (ponderomotive) force fNL resulting in ultra-fast expanding plasma blocks by a dielectric explosion. Combining this with measured ultrahigh magnetic fields and the avalanche process opens an option for an environmentally absolute clean and economic boron fusion power reactor. This is supported also by other experiments with very high HB11 reactions under different conditions (Labaune et al., Nature Commun. 4, 2506 (2013)).
PDF全文 (下载：71) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e35
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The Z-backlighter laser facility primarily consists of two high energy, high-power laser systems. Z-Beamlet laser (ZBL) (Rambo et al., Appl. Opt. 44, 2421 (2005)) is a multi-kJ-class, nanosecond laser operating at 1054 nm which is frequency doubled to 527 nm in order to provide x-ray backlighting of high energy density events on the Z-machine. Z-Petawatt (ZPW) (Schwarz et al., J. Phys.: Conf. Ser. 112, 032020 (2008)) is a petawatt-class system operating at 1054 nm delivering up to 500 J in 500 fs for backlighting and various short-pulse laser experiments (see also Figure 10 for a facility overview).With the development of the magnetized liner inertial fusion (MagLIF) concept on the Z-machine, the primary backlighting missions of ZBL and ZPW have been adjusted accordingly. As a result, we have focused our recent efforts on increasing the output energy of ZBL from 2 to 4 kJ at 527 nm by modifying the fiber front end to now include extra bandwidth (for stimulated Brillouin scattering suppression). The MagLIF concept requires a well-defined/behaved beam for interaction with the pressurized fuel. Hence we have made great efforts to implement an adaptive optics system on ZBL and have explored the use of phase plates. We are also exploring concepts to use ZPW as a backlighter for ZBL driven MagLIF experiments. Alternatively, ZPW could be used as an additional fusion fuel pre-heater or as a temporally flexible high energy pre-pulse. All of these concepts require the ability to operate the ZPW in a nanosecond long-pulse mode, in which the beam can co-propagate with ZBL. Some of the proposed modifications are complete and most of them are well on their way.
PDF全文 (下载：51) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e36
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A diode-pumped alkali laser (DPAL) provides the significant promise for high-powered performances. In this paper, a mathematical model is introduced for examination of the kinetic processes of a diode-pumped cesium vapor hollow-core photonic-crystal fiber (HC-PCF) laser, in which the cesium vapor is filled in the center hole of a photonic-bandgap fiber instead of a glass cell. The influence of deleterious processes including energy pooling, photo-ionization, and Penningionization on the physical features of a fiber DPAL is studied in this report. It has been theoretically demonstrated that the deleterious processes cannot be ignored in a high-powered fiber-DPAL system.
PDF全文 (下载：95) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e37
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A diode-pumped alkali vapor laser (DPAL) is one of the most promising candidates of the next-generation high-powered laser source. As the saturated number density of alkali vapor is highly dependent on the temperature inside a vapor cell, the temperature distribution in the cross-section of a cell will greatly affect the homogeneity of a laser medium and the output characteristics of a DPAL. In this paper, we developed an algorithm based on the regime concluding quasi-Hilbert transform to evaluate the phase aberration of a wavefront when the probe beam passes through the vapor cell placed in one arm of a Mach–Zehnder interference setup. According to the theoretical algorithm, we deduced the temperature distribution of a cesium vapor cell for different heating conditions. The study is thought to be useful for development of a high-powered laser.
PDF全文 (下载：61) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e38
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We report on the temporal contrast performance of the PHELIX facility in view of the requirements imposed by solidtarget interaction experiments. The requirement analysis for the nanosecond and picosecond temporal contrast is derived from empirical data and simple theoretical modeling, while the realization shows that using an ultrafast optical parametric amplifier and plasma mirrors enables meeting this specification.
PDF全文 (下载：72) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e39
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We report on the observation of subcycle interferences of electron wave packets released during strong field ionization of H2 with cycle-shaped two-color laser fields. With a reaction microscope we measure three-dimensional momentum distributions of photoelectrons correlated with either HC2 or protons within different energy ranges generated by dissociation of HC2 . We refer to these different types of photoelectrons as channels. Our results show that the subcycle interference structures of electron wave packets are very sensitive to the cycle shape of the two-color laser field. We explain this behavior by the dependence of the ionization time within an optical cycle on the shape of the laser field cycle. The subcycle interference structures can be further used to obtain insight into the subcycle dynamics of molecules during strong field interaction.
PDF全文 (下载：51) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e40
S. D. Moustaizis
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Numerical estimates for electrons and mesons particle–antiparticle creation from vacuum in the presence of strong electromagnetic fields are derived, using the complete probability density relation of Popov’s imaginary time method (Popov, JETP Lett. 13, 185 (1971); Sov. Phys. JETP 34, 709 (1972); Sov. Phys. JETP 35, 659 (1972); Popov and Marinov, Sov. J. Nucl. Phys. 16, 449 (1973); JETP Lett. 18, 255 (1974); Sov. J. Nucl. Phys. 19, 584 (1974)); (Popov, Phys. Let. A 298, 83 (2002)), and within the framework of an experimental setup like the E144 (Burke et al., Phys. Rev. Lett. 79, 1626 (1997)). The existence of crossing point among pair creation efficiency curves of different photon energies and the role of odd/even multiphoton orders in the production rates are discussed. Finally a kind of tunability processbetween the two creation processes is discussed.
PDF全文 (下载：57) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e41
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The application of laser pulses with psec or shorter duration enables nonthermal efficient ultrahigh acceleration of plasma blocks with homogeneous high ion energies exceeding ion current densities of 1012 A cm??2. The effects of ultrahigh acceleration of plasma blocks with high energy proton beams are proposed for muon production in a compact magnetic fusion device. The proposed new scheme consists of an ignition fusion spark by muon catalyzed fusion (mCF) in a small mirror-like configuration where low temperature D–T plasma is trapped for a duration of 1 ms. This initial fusion spark produces sufficient alpha heating in order to initiate the fusion process in the main device. The use of a multi-fluid global particle and energy balance code allows us to follow the temporal evolution of the reaction rate of the fusion process in the device. Recent progress on the ICAN and IZEST projects for high efficient high power and high repetition rate laser systems allows development of the proposed device for clean energy production. With the proposed approaches, experiments on fusion nuclear reactions and mCF process can be performed in magnetized plasmas in existing kJ=PW laser facilities as the GEKKO-LFEX, the PETAL and the ORION or in the near future laser facilities as the ELI-NP Romanian pillar.
PDF全文 (下载：53) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e42
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We demonstrate a high-contrast, joule-level Nd:glass laser system operating at 0.5 Hz repetition rate based on a double chirped pulse amplification (CPA) scheme. By injecting high-contrast, high-energy seed pulses into the Nd:glass CPA stage, the pulse energy is amplified to 1.9 J through two optical parametric CPA stages and two Nd:glass amplifiers. The temporal contrast of compressed pulse is measured down to the level of 10??8 at tens of ps, and 10??10 near 200 ps beforethe main pulse, respectively.
PDF全文 (下载：57) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e43
J. L. Kline
S. A. Yi
A. N. Simakov
R. E. Olson
D. C. Wilson
G. A. Kyrala
T. S. Perry
S. H. Batha
E. L. Dewald
J. E. Ralph
D. J. Strozzi
A. G. MacPhee
D. A. Callahan
O. A. Hurricane
R. J. Leeper
A. B. Zylstra
R. R. Peterson
B. M. Haines
P. A. Bradley
R. C. Shah
B. J. Kozioziemski
J. D. Sater
M. M. Biener
A. V. Hamza
L. F. Berzak Hopkins
N. B. Meezan
D. S. Montgomery
W. S. Daughton
E. C. Merritt
E. S. Dodd
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Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting features appear to be two key limiting factors for implosion performance. One reason these factors have a large impact on the performance of inertial confinement fusion implosions is the high convergence required to achieve high fusion gains. To tackle these problems, a predictable implosion platform is needed meaning experiments must trade-off high gain for performance. LANL has adopted three main approaches to develop a one-dimensional (1D) implosion platform where 1D means measured yield over the 1D clean calculation. A high adiabat, low convergence platform is being developed using beryllium capsules enabling larger case-to-capsule ratios to improve symmetry. The second approach is liquid fuel layers using wetted foam targets.With liquid fuel layers, the implosion convergence can be controlled via the initial vapor pressure set by the target fielding temperature. The last method is double shell targets. For double shells, the smaller inner shell houses the DT fuel and the convergence of this cavity is relatively small compared to hot spot ignition. However, double shell targets have a different set of trade-off versus advantages. Details for each of these approaches are described.
PDF全文 (下载：57) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e44
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Using the example of the PHELIX high-energy short pulse laser we discuss the technical preconditions to investigate ion acceleration with submicrometer thick targets. We show how the temporal contrast of this system was improved to prevent pre-ionization of such targets on the nanosecond timescale. Furthermore the influence of typical fluctuations or uncertainties of the on-target intensity on ion acceleration experiments is discussed. We report how these uncertainties were reduced by improving the assessment and control of the on-shot intensity and by optimizing the positioning of the target into the focal plane. Finally we report on experimental results showing maximum proton energies in excess of 85 MeV for ion acceleration via the target normal sheath acceleration mechanism using target thicknesses on the order of one micrometer.
PDF全文 (下载：60) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e45
J. P. Colombier
We discuss the dynamics of ultrashort pulsed laser excitation in bulk optical silica-based glasses (fused silica and borosilicate BK7) well-above the permanent modification threshold. We indicate subsequent structural and thermomechanical energy relaxation paths that translate into positive and negative refractive index changes, compression and rarefaction zones. If fast electronic decay occurs at low excitation levels in fused silica via self-trapping of excitons, for carrier densities in the vicinity of the critical value at the incident wavelength, persistent long-living absorptive states indicate the achievement of low viscosity matter states manifesting pressure relaxation, rarefaction, void opening and compaction in the neighboring domains. An intermediate ps-long excited carrier dynamics is observed for BK7 in the range corresponding to structural expansion and rarefaction. The amount of excitation and the strength of the subsequent hydrodynamic evolution is critically dependent on the pulse time envelope, indicative of potential optimization schemes.
PDF全文 (下载：49) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.e46
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PDF全文 (下载：0) High Power Laser Science and Engineering ，2016年第4卷第4期 pp.1-2