A collective, macroscopic signature to detect radiation friction in laser-plasma experiments is proposed. In the interaction of superintense circularly polarized laser pulses with high density ...targets, the effective dissipation due to radiative losses allows the absorption of electromagnetic angular momentum, which in turn leads to the generation of a quasistatic axial magnetic field. This peculiar 'inverse Faraday effect' is investigated by analytical modeling and three-dimensional simulations, showing that multi-gigagauss magnetic fields may be generated at laser intensities > 10 23 W cm − 2 .
The acceleration of ions from ultrathin foils has been investigated by using 250 TW, subpicosecond laser pulses, focused to intensities of up to 3 × 10(20) W cm(-2). The ion spectra show the ...appearance of narrow-band features for protons and carbon ions peaked at higher energies (in the 5-10 MeV/nucleon range) and with significantly higher flux than previously reported. The spectral features and their scaling with laser and target parameters provide evidence of a multispecies scenario of radiation pressure acceleration in the light sail mode, as confirmed by analytical estimates and 2D particle-in-cell simulations. The scaling indicates that monoenergetic peaks with more than 100 MeV/nucleon are obtainable with moderate improvements of the target and laser characteristics, which are within reach of ongoing technical developments.
The acceleration of ions from ultrathin (10-100 nm) carbon foils has been investigated using intense (∼6×10^{20} W cm^{-2}) ultrashort (45 fs) laser pulses, highlighting a strong dependence of the ...ion beam parameters on the laser polarization, with circularly polarized (CP) pulses producing the highest energies for both protons and carbons (25-30 MeV/nucleon); in particular, carbon ion energies obtained employing CP pulses were significantly higher (∼2.5 times) than for irradiations employing linearly polarized pulses. Particle-in-cell simulations indicate that radiation pressure acceleration becomes the dominant mechanism for the thinnest targets and CP pulses.
Abstract
Surface plasmon (SP) excitation in intense laser interaction with solid target can be exploited for enhancing secondary emissions, in particular efficient acceleration of high charge ...electron bunches. Previous studies have mostly used grating coupling to allow SP excitation, which requires stringent laser contrast conditions to preserve the structural integrity of the target. Here we show via simulations that efficient SP electron acceleration for currently available short pulse lasers can occur in a flat foil irradiated at parallel or grazing incidence (
∼
5
°
with the target surface) without a surface modulation. In turn, the accelerated electrons can be effective for generating proton beams with narrow spectra peaked at
>
100 MeV energies for currently available laser drivers.
In the interaction of laser pulses of extreme intensity (>1023 Wcm−2) with high-density, thick plasma targets, simulations show significant radiation friction losses, in contrast to thin targets for ...which such losses are negligible. We present an analytical calculation, based on classical radiation friction modeling, of the conversion efficiency of the laser energy into incoherent radiation in the case when a circularly polarized pulse interacts with a thick plasma slab of overcritical initial density. By accounting for three effects including the influence of radiation losses on the single electron trajectory, the global 'hole boring' motion of the laser-plasma interaction region under the action of radiation pressure, and the inhomogeneity of the laser field in both longitudinal and transverse direction, we find a good agreement with the results of three-dimensional particle-in-cell simulations. Overall, the collective effects greatly reduce radiation losses with respect to electrons driven by the same laser pulse in vacuum, which also shift the reliability of classical calculations up to higher intensities.
Abstract Objectives This work focuses on a titanium alloy implants incorporating a gradient of porosity, from the inner core to the outer surface, obtained by laser sintering of metal powder. Surface ...appearance, microstructure, composition, mechanical properties and fractography were evaluated. Methods All the specimens were prepared by a selective laser sintering procedure using a Ti–6Al–4V alloy powder with a particle size of 1–10 μm. The morphological and chemical analyses were performed by SEM and energy dispersive X-ray spectroscopy. The flexure strength was determined by a three-point bend test using a universal testing machine. The surface roughness was investigated using a confocal scanning laser microscope. The surface roughness variation was statistically evaluated by use of a Chi square test. A p value of <0.05 was considered statistically significant. Results The original surface microstructure consisted of roughly spherical particles, diameter range 5–50 μm. After exposure to hydrofluoric acid some of these were removed and the microsphere diameter then ranged from 5.1 μm to 26.8 μm. Following an organic acid treatment, particles were replaced by grooves 14.6–152.5 μm in width and 21.4–102.4 μm depth. The metal core consisted of columnar beta grains with alpha and beta laths within the grains. The alloy was composed of 90.08% Ti, 5.67% Al and 4.25% V. The Young's modulus of the inner core material was 104 ± 7.7 GPa; while that of the outer porous material was 77 ± 3.5 GPa. The fracture face showed a dimpled appearance typical of ductile fracture. Significance In conclusion, laser metal sintering proved to be an efficient means of construction of dental implants with a functionally graded material which is better adapted to the elastic properties of the bone. Such implants should minimize stress shielding effects and improve long-term performance.
The generation of energetic electron bunches by the interaction of a short, ultraintense (I>10(19) W/cm(2)) laser pulse with "grating" targets has been investigated in a regime of ultrahigh ...pulse-to-prepulse contrast (10(12)). For incidence angles close to the resonant condition for surface plasmon excitation, a strong electron emission was observed within a narrow cone along the target surface, with energy spectra peaking at 5-8 MeV and total charge of ∼100 pC. Both the energy and the number of emitted electrons were strongly enhanced with respect to simple flat targets. The experimental data are closely reproduced by three-dimensional particle-in-cell simulations, which provide evidence for the generation of relativistic surface plasmons and for their role in driving the acceleration process. Besides the possible applications of the scheme as a compact, ultrashort source of MeV electrons, these results are a step forward in the development of high-field plasmonics.
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