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Abstract Spontaneous magnetic field generation plays important role in laser-plasma interactions. Strong quasi-static magnetic fields affect the thermal conductivity and the plasma dynamics, particularly in the case of ultra intense laser where the magnetic part of Lorentz force becomes as significant as the electric part. Kinetic simulations of giga-gauss magnetic field amplification via a laser irradiated microtube structure reveal the dynamics of charged particle implosions and the mechanism of magnetic field growth. A giga-gauss magnetic field is generated and amplified with the opposite polarity to the seed magnetic field. The spot size of the field is comparable to the laser wavelength, and the lifetime is hundreds of femtoseconds. An analytical model is presented to explain the underlying physics. This study should aid in designing future experiments.

The thermal and epithermal neutrons are powerful probes to inspect water or high-pressure hydrogen gas because of their large scattering cross-sections with protons. Laser-driven neutron source, which is able to simultaneously emit different types of radiations such as x rays, can be used for neutron and x-ray radiography in the same laser shot. In this paper, we report the demonstration of non-destructive inspection for H2O contained within a stainless steel pipe using a laser-driven thermal neutron source, where water and stainless containers are detected by neutrons and x rays, respectively. The simulation result indicates that this method can also provide the capability to measure the hydrogen density in high-pressure hydrogen gas in metal containers.

Optimum laser configurations are presented to achieve high illumination uniformity with directly driven inertial confinement fusion targets. Assuming axisymmetric absorption pattern of individual laser beams, theoretical models are reviewed in terms of the number of laser beams, system imperfection, and laser beam patterns. Utilizing a self-organizing system of charged particles on a sphere, a simple numerical model is provided to give an optimal configuration for an arbitrary number of laser beams. As a result, such new configurations as “M48” and “M60” are found to show substantially higher illumination uniformity than any other existing direct drive systems. A new polar direct-drive scheme is proposed with the laser axes keeping off the target center, which can be applied to laser configurations designed for indirectly driven inertial fusion.

The interaction of micro-bubbles with ultra-intense laser pulses has been shown to generate ultra-high proton densities and correspondingly high electric fields. We investigate the possibility of using such a combination to study the fundamental physical phenomenon of vacuum polarization. With current or near-future laser systems, measurement of vacuum polarization via the bending of gamma rays that pass near imploded micro-bubbles may be possible. Since it is independent of photon energy to within the leading-order solution of the Heisenberg–Euler Lagrangian and the geometric optics approximation, the corresponding index of refraction can dominate the indices of refraction due to other effects at sufficiently high photon energies. We consider the possibility of its application to a transient gamma-ray lens.

We present a comparative study on the hydrodynamic behaviour of plasmas generated by material ablation by the irradiation of nanosecond extreme ultraviolet (EUV or XUV) or infrared laser pulses on solid samples. It was clarified that the difference in the photon energy deposition and following material heating mechanism between these two lights result in the difference in the plasma parameters and plasma expansion characteristics. Silicon plate was ablated by either focused intense EUV pulse (λ=9-25 nm, 10 ns) or laser pulse (λ=1064 nm, 10 ns), both with an intensity of ~109W/cm². Both the angular distributions and energy spectra of the expanding ions revealed that the photoionized plasma generated by the EUV light differs significantly from that produced by the laser. The laser-generated plasma undergoes spherical expansion, whereas the EUV-generated plasma undergoes planar expansion in a comparatively narrow angular range. It is presumed that the EUV radiation is transmitted through the expanding plasma and directly photoionizes the samples in the solid phase, consequently forming a high-density and high-pressure plasma. Due to a steep pressure gradient along the direction of the target normal, the EUV plasma expands straightforward resulting in the narrower angular distribution observed. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet (EUV) emission from Xe plasma in the λ=13.5 nm band is theoretically investigated for lithographic application. It appears that a large number of satellite lines due to the 4d–4f, 4d–5p, and 4p–4d transitions significantly contribute to the emission over the spectral range from 10 to 17 nm. At electron densities above 1020/cm3, laser-produced Xe plasmas attain quasilocal thermodynamic equilibrium (LTE) in order to make the emission intensity in the 13.5 nm band comparable to that in the 11 nm band. [ABSTRACT FROM AUTHOR]

Enhanced laser-driven proton acceleration occurs when an intense laser interacts with a transversely nano-striped target consisted of alternate gold and hydrogen stripes. The density of the laser-irradiated hydrogen stripes initially decreases to less than the critical density, enabling the laser field to penetrate into the hydrogen stripes and heat the electrons in the still-opaque gold stripes. The resulting increase in the electron Lorentz factor and the expansion of all the electrons ultimately make the entire target relativistically transparent to the latter part of the laser beam. Large numbers of hot electrons are expelled from the target because the laser volumetrically interacts with the whole target. A fairly high electrostatic field is then induced on the rear side of the target to accelerate the protons. When compared with double-layer or single-layer targets, the proton acceleration is much more efficient in the relativistically transparent nano-striped target presented here. Two spatial and three velocity dimensions (2D3V) particle-in-cell simulations show that with an W cm−2 laser, a proton beam with a maximum energy of approximately 190 MeV can be generated. [ABSTRACT FROM AUTHOR]

The interaction of dense plasmas with an intense laser under a strong external magnetic field has been investigated. When the cyclotron frequency for the ambient magnetic field is higher than the laser frequency, the laser's electromagnetic field is converted to the whistler mode that propagates along the field line. Because of the nature of the whistler wave, the laser light penetrates into dense plasmas with no cutoff density, and produces superthermal electrons through cyclotron resonance. It is found that the cyclotron resonance absorption occurs effectively under the broadened conditions, or a wider range of the external field, which is caused by the presence of relativistic electrons accelerated by the laser field. The upper limit of the ambient field for the resonance increases in proportion to the square root of the relativistic laser intensity. The propagation of a large-amplitude whistler wave could raise the possibility for plasma heating and particle acceleration deep inside dense plasmas. [ABSTRACT FROM AUTHOR]