Control of the collective response of plasma particles to intense laser light is intrinsic to relativistic optics, the development of compact laser-driven particle and radiation sources, as well as ...investigations of some laboratory astrophysics phenomena. We recently demonstrated that a relativistic plasma aperture produced in an ultra-thin foil at the focus of intense laser radiation can induce diffraction, enabling polarization-based control of the collective motion of plasma electrons. Here we show that under these conditions the electron dynamics are mapped into the beam of protons accelerated via strong charge-separation-induced electrostatic fields. It is demonstrated experimentally and numerically via 3D particle-in-cell simulations that the degree of ellipticity of the laser polarization strongly influences the spatial-intensity distribution of the beam of multi-MeV protons. The influence on both sheath-accelerated and radiation pressure-accelerated protons is investigated. This approach opens up a potential new route to control laser-driven ion sources.
Abstract
Interaction of intense lasers with nm thick targets provides an attractive regime for the acceleration of ions of all types. Acceleration of heavy ions however is undermined in the presence ...of low charge contaminant species due to their higher charge-to-mass ratio. Here we show narrow-band acceleration of very heavy Au ions from ~15 nm Au foils driven by a sub-Petawatt laser, with spectral peaks of 1.5 ± 0.5 GeV at fluxes on the order of 10
12
particles per steradian. 3D and 2D particle-in-cell simulations show a complex interplay between different acceleration mechanisms at different stages of the interaction, suggesting the spectrally peaked Au ion bunches stem from strong radiation pressure acceleration on a heavy-ion dominant plasma in the moments just before transparency, followed by an efficient acceleration due to transparency-enhanced mechanisms.
The measured spatial-intensity distribution of the beam of protons accelerated from the rear side of a solid target irradiated by an intense (>1019 Wcm−2) laser pulse provides a diagnostic of the ...two-dimensional fast electron density profile at the target rear surface and thus the fast electron beam transport pattern within the target. An analytical model is developed, accounting for rear-surface fast electron sheath dynamics, ionization and projection of the resulting beam of protons. The sensitivity of the spatial-intensity distribution of the proton beam to the fast electron density distribution is investigated. An annular fast electron beam transport pattern with filamentary structure is inferred for the case of a thick diamond target irradiated at a peak laser intensity of 6 × 1019 Wcm−2.
To determine whether gatifloxacin 0.3% ophthalmic solution or moxifloxacin 0.5% ophthalmic solutions are toxic to the corneal epithelium when used with 1 of 2 dosing regimens in healthy human eyes.
...Price Vision Group, Indianapolis, Indiana, USA.
In this double-masked randomized fellow-eye comparison study, gatifloxacin 0.3% was instilled in 1 eye and moxifloxacin 0.5% in the other eye either 4 times a day for 7 days or hourly for 10 hours. Before and after dosing, all eyes were examined with a slitlamp and the cell layers in the central cornea were evaluated by confocal microscopy. Subject discomfort with study drop instillation was also assessed.
There was no statistically significant increase in the incidence or severity of superficial punctuate keratitis following use of gatifloxacin 0.3% or moxifloxacin 0.5% when instilled 4 times a day for 7 days or hourly for 10 hours. Hourly use of gatifloxacin 0.3% for 10 hours resulted in a mild but statistically significant increase in conjunctival hyperemia (P = .029). Use of moxifloxacin 0.5% resulted in a small but statistically significant deterioration of the corneal epithelial surface as assessed by confocal microscopy (P = .045). The incidence of subject discomfort with study drop instillation was comparable for the 2 antibiotics (P = .67).
Use of ophthalmic solutions of gatifloxacin 0.3% or moxifloxacin 0.5% did not result in clinically significant epithelial toxicity in healthy human corneas after dosing regimens of 4 times a day for 7 days or hourly for 10 hours dosing regimens.
The collective response of electrons in an ultrathin foil target irradiated by an ultraintense (${\sim}6\times 10^{20}~\text{W}~\text{cm}^{-2}$) laser pulse is investigated experimentally and via 3D ...particle-in-cell simulations. It is shown that if the target is sufficiently thin that the laser induces significant radiation pressure, but not thin enough to become relativistically transparent to the laser light, the resulting relativistic electron beam is elliptical, with the major axis of the ellipse directed along the laser polarization axis. When the target thickness is decreased such that it becomes relativistically transparent early in the interaction with the laser pulse, diffraction of the transmitted laser light occurs through a so called ‘relativistic plasma aperture’, inducing structure in the spatial-intensity profile of the beam of energetic electrons. It is shown that the electron beam profile can be modified by variation of the target thickness and degree of ellipticity in the laser polarization.
This thesis reports on experimental and numerical investigations of relativistic electron transport in solids irradiated by intense (i.e. IL > 10p19s Wcmp-2s) laser pulses. Specifically, the effect ...of electrical resistivity on fast electron transport is explored. The first investigation explores fast electron transport in allotropes of carbon by measuring the spatial-intensity distribution of the beam of protons accelerated from the target rear-surface. An analytical model is developed which accounts for the rear-surface fast electron sheath dynamics, ionisation and projection of the resulting beam of protons, and is used (in conjunction with the experimental measurements) to infer annular fast electron beam transport with lamentary structure in 200 um-thick diamond targets. The important role that material lattice structure has in defining electrical resistivity, which in turn defines the fast electron transport properties, is established utilising three-dimensional hybrid pa rticle-in-cell (3D hybrid-PIC) simulations together with an analytical model of the resistive lamentation instability. The second investigation explores fast electron transport in silicon utilising both experimental measurements and 3D hybrid-PIC simulations. Annular fast electron transport is demonstrated and explained by resistively generated magnetic fields. The results indicate the potential to completely transform the beam transport pattern by tailoring the resistivity-temperature profile at temperatures as low as a few eV. Additionally, the sensitivity of annular fast electron beam transport is explored by varying the drive laser pulse parameters (i.e. energy, focal spot radius and pulse duration) and is found to be particularly sensitive to the peak laser pulse intensity. An ability to optically 'tune' the properties of an annular fast electron transport pattern may be important for applications. In the final investigation the effect that initial target temperature, and thus lattice melt, has on fast electron transport properties is demonstrated. Laser-accelerated proton beams are used to isochorically heat silicon for several tens-of-picoseconds prior to the propagation of fast electrons through the pre-heated target. This enables the influence of resistivity gradients, generated by proton-induced lattice melt, on fast electron transport properties to be explored. The experimental observation of an annular proton beam after t heat = 30 ps of proton pre-heating, which corresponds to annular electron transport within the target, is in excellent qualitative agreement with 3-D hybrid-PIC simulations of fast electron transport in a target containing an initial temperature (and thus, resistivity) gradient.
This thesis reports on experimental and numerical investigations of relativistic electron transport in solids irradiated by intense (i.e. IL > 10p19s Wcmp-2s) laser pulses. Specifically, the effect ...of electrical resistivity on fast electron transport is explored. The first investigation explores fast electron transport in allotropes of carbon by measuring the spatial-intensity distribution of the beam of protons accelerated from the target rear-surface. An analytical model is developed which accounts for the rear-surface fast electron sheath dynamics, ionisation and projection of the resulting beam of protons, and is used (in conjunction with the experimental measurements) to infer annular fast electron beam transport with lamentary structure in 200 um-thick diamond targets. The important role that material lattice structure has in defining electrical resistivity, which in turn defines the fast electron transport properties, is established utilising three-dimensional hybrid pa rticle-in-cell (3D hybrid-PIC) simulations together with an analytical model of the resistive lamentation instability. The second investigation explores fast electron transport in silicon utilising both experimental measurements and 3D hybrid-PIC simulations. Annular fast electron transport is demonstrated and explained by resistively generated magnetic fields. The results indicate the potential to completely transform the beam transport pattern by tailoring the resistivity-temperature profile at temperatures as low as a few eV. Additionally, the sensitivity of annular fast electron beam transport is explored by varying the drive laser pulse parameters (i.e. energy, focal spot radius and pulse duration) and is found to be particularly sensitive to the peak laser pulse intensity. An ability to optically 'tune' the properties of an annular fast electron transport pattern may be important for applications. In the final investigation the effect that initial target temperature, and thus lattice melt, has on fast electron transport properties is demonstrated. Laser-accelerated proton beams are used to isochorically heat silicon for several tens-of-picoseconds prior to the propagation of fast electrons through the pre-heated target. This enables the influence of resistivity gradients, generated by proton-induced lattice melt, on fast electron transport properties to be explored. The experimental observation of an annular proton beam after t heat = 30 ps of proton pre-heating, which corresponds to annular electron transport within the target, is in excellent qualitative agreement with 3-D hybrid-PIC simulations of fast electron transport in a target containing an initial temperature (and thus, resistivity) gradient.
The development of a new approach towards the evaluation of school systems comes at a time when questions of accountability are being directed at the public school system. District school boards and ...administrators are being pressured to ensure that school systems are responsive to the needs of those they are designed to serve; as a result, increasing demands have arisen for an evaluation process to provide advice and insight to administrators for improvement, change, and growth. This study posits a new approach to school system evaluation, the LINC interactive Model. The model is conceptualized from a review of the literature pertaining to evaluation and school systems: educational evaluation literature/models, organizational effectiveness literature/studies, school systems literature/studies, and effective schools literature/studies. Four domains (L.I.N.C.) of thirteen specific components, eclectically identified from the research and ranked according to their permanence, prominence, and frequency in the above sources, provide an evaluation process for assessing school systems. Each of the thirteen components is defined and a checklist/guide given to aid an evaluator in assessing a school system. An analysis and comparison of the new model with the evaluation models of leading theorists and its application to three of the twenty-eight Nova Scotia school system reviews conducted from 1978-1991 serve as a mirror by which this new approach can be tested. The uniqueness of the LINC interactive Model, is its focus on the school system as a fundamental social system, operating effectively as a collective entity of all of its interdependent and interactive components, highly specialized and functioning together for common goals.
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