| 1. |
- Pirozhkov, A. S., et al.
(author)
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Diagnostic of laser contrast using target reflectivity
- 2009
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:24
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Journal article (peer-reviewed)abstract
- Using three different laser systems, we demonstrate a convenient and simple plasma based diagnostic of the contrast of high-power short-pulse lasers. The technique is based on measuring the specular reflectivity from a solid target. The reflectivity remains high even at relativistic intensities above 10(19) W/cm(2) in the case of a high-contrast prepulse-free laser. On the contrary, the specular reflectivity drops with increasing intensities in the case of systems with insufficient contrast due to beam breakup and increased absorption caused by preplasma.
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| 2. |
- McKenna, P., et al.
(author)
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Effects of front surface plasma expansion on proton acceleration in ultraintense laser irradiation of foil targets
- 2008
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In: Laser and Particle Beams. - 0263-0346. ; 26:4, s. 591-596
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Journal article (peer-reviewed)abstract
- The properties of beams of high energy protons accelerated during ultraintense, picosecond laser-irradiation of thin foil targets are investigated as a function of preplasma expansion at the target front surface. Significant enhancement in the maximum proton energy and laser-to-proton energy conversion efficiency is observed at optimum preplasma density gradients due, to self-focusing Of the incident laser pulse. For very long preplasma expansion, the propagating laser pulse is observed to filament, resulting in highly uniform proton beams, but with reduced flux and maximum energy.
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| 3. |
- Robinson, A. P. L., et al.
(author)
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Spectral modification of laser-accelerated proton beams by self-generated magnetic fields
- 2009
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11
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Journal article (peer-reviewed)abstract
- Target normal measurements of proton energy spectra from ultrathin (50-200 nm) planar foil targets irradiated by 10(19) W cm(-2) 40 fs laser pulses exhibit broad maxima that are not present in the energy spectra from micron thickness targets (6 mu m). The proton flux in the peak is considerably greater than the proton flux observed in the same energy range in thicker targets. Numerical modelling of the experiment indicates that this spectral modification in thin targets is caused by magnetic fields that grow at the rear of the target during the laser-target interaction.
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| 4. |
- Carroll, DC, et al.
(author)
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Active manipulation of the spatial energy distribution of laser-accelerated proton beams
- 2007
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In: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 76:065401(R), s. 1-065401
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Journal article (peer-reviewed)abstract
- The spatial energy distributions of beams of protons accelerated by ultrahigh intensity (>10^19 W/cm2) picosecond laser pulse interactions with thin foil targets are investigated. Using separate, low intensity (<10^13 W/cm2) nanosecond laser pulses, focused onto the front surface of the target foil prior to the arrival of the high intensity pulse, it is demonstrated that the proton beam profile can be actively manipulated. In particular, results obtained with an annular intensity distribution at the focus of the low intensity beam are presented, showing smooth proton beams with a sharp circular boundary at all energies, which represents a significant improvement in the beam quality compared to irradiation with the picosecond beam alone.
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| 5. |
- Clarke, R. J., et al.
(author)
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Detection of short lived radioisotopes as a fast diagnostic for intense laser-solid interactions
- 2006
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:14
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Journal article (peer-reviewed)abstract
- As a diagnostic of high-intensity laser interactions (> 10(19) W cm(-2)), the detection of radioactive isotopes is regularly used for the characterization of proton, neutron, ion, and photon beams. This involves sample removal from the interaction chamber and time consuming post shot analysis using NaI coincidence counting or Ge detectors. This letter describes the use of in situ detectors to measure laser-driven (p,n) reactions in Al-27 as an almost real-time diagnostic for proton acceleration. The produced Si-27 isotope decays with a 4.16 s half-life by the predominantly beta+ emission, producing a strong 511 keV annihilation peak. (c) 2006 American Institute of Physics.
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| 6. |
- Kar, S., et al.
(author)
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Guiding of Relativistic Electron Beams in Solid Targets by Resistively Controlled Magnetic Fields
- 2009
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In: Physical Review Letters. - 1079-7114. ; 102:5
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Journal article (peer-reviewed)abstract
- Guided transport of a relativistic electron beam in solid is achieved experimentally by exploiting the strong magnetic fields created at the interface of two metals of different electrical resistivities. This is of substantial relevance to the Fast Ignitor approach to fusion energy production [M. Tabak et al., Phys. Plasmas 12, 057305 (2005)], since it allows the electron deposition to be spatially tailored-thus adding substantial design flexibility and preventing inefficiencies due to electron beam spreading. In the experiment, optical transition radiation and thermal emission from the target rear surface provide a clear signature of the electron confinement within a high resistivity tin layer sandwiched transversely between two low resistivity aluminum slabs. The experimental data are found to agree well with numerical simulations.
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| 7. |
- McKenna, P., et al.
(author)
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Lateral electron transport in high-intensity laser-irradiated foils diagnosed by ion emission
- 2007
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In: Physical Review Letters. - 1079-7114. ; 98:14
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Journal article (peer-reviewed)abstract
- An experimental investigation of lateral electron transport in thin metallic foil targets irradiated by ultraintense (>= 10(19) W/cm(2)) laser pulses is reported. Two-dimensional spatially resolved ion emission measurements are used to quantify electric-field generation resulting from electron transport. The measurement of large electric fields (similar to 0.1 TV/m) millimeters from the laser focus reveals that lateral energy transport continues long after the laser pulse has decayed. Numerical simulations confirm a very strong enhancement of electron density and electric field at the edges of the target.
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| 8. |
- McKenna, P, et al.
(author)
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Low- and medium-mass ion acceleration driven by petawatt laser plasma interactions
- 2007
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In: Plasma Physics and Controlled Fusion. - 0741-3335. ; 49:B223, s. 223-231
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Journal article (peer-reviewed)abstract
- An experimental investigation of low- and medium-mass ion acceleration from resistively heated thin foil targets, irradiated by picosecond laser pulses at intensities up to 5 × 10^20 Wcm−2, is reported. It is found that the spectral distributions of ions, up to multi-MeV/nucleon energies, accelerated from the rear surface of the target are broadly consistent with previously reported measurements made at intensities up to 5 × 10^19 Wcm−2. Properties of the backward-directed beams of ions accelerated from the target front surface are also measured, and it is found that, compared with the rear surface, higher ion numbers and charges, and similar ion energies are produced. Additionally, the scaling of the maximum ion energy as a function of ion charge and laser intensity are measured and compared with the predictions of a numerical model.
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| 9. |
- Robson, L, et al.
(author)
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Scaling of proton acceleration driven by petawatt-laser-plasma interactions
- 2007
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In: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 3:58, s. 58-62
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Journal article (peer-reviewed)abstract
- The possibility of using high-power lasers to generate high-quality beams of energetic ions is attracting large global interest. The prospect of using laser-accelerated protons in medicine attracts particular interest, as these schemes may lead to compact and relatively low-cost sources. Among the challenges remaining before these sources can be used in medicine is to increase the numbers and energies of the ions accelerated. Here, we extend the energy and intensity range over which proton scaling is experimentally investigated, up to 400 J and 6×10^20 Wcm−2 respectively, and find a slower proton scaling than previously predicted. With the aid of plasma-expansion simulation tools, our results suggest the importance of time-dependent andmultidimensional effects in predicting the maximum proton energy in this ultrahigh-intensity regime. The implications of our new understanding of proton scaling for potential medical applications are discussed.
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