An intense collimated beam of high-energy protons is emitted normal to the rear surface of thin solid targets irradiated at 1 PW power and peak intensity 3x10(20) W cm(-2). Up to 48 J ( 12%) of the laser energy is transferred to 2x10(13) protons of energy >10 MeV. The energy spectrum exhibits a sharp high-energy cutoff as high as 58 MeV on the axis of the beam which decreases in energy with increasing off axis angle. Proton induced nuclear processes have been observed and used to characterize the beam.

Intense High-Energy Proton Beams from Petawatt-Laser Irradiation of Solids

The advent of ultraintense laser pulses generated by the technique of chirped pulse amplification (CPA) along with the development of high-fluence laser materials has opened up an entirely new field of optics. The electromagnetic field intensities produced by these techniques, in excess of ${10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, lead to relativistic electron motion in the laser field. The CPA method is reviewed and the future growth of laser technique is discussed, including the prospect of generating the ultimate power of a zettawatt. A number of consequences of relativistic-strength optical fields are surveyed. In contrast to the nonrelativistic regime, these laser fields are capable of moving matter more effectively, including motion in the direction of laser propagation. One of the consequences of this is wakefield generation, a relativistic version of optical rectification, in which longitudinal field effects could be as large as the transverse ones. In addition to this, other effects may occur, including relativistic focusing, relativistic transparency, nonlinear modulation and multiple harmonic generation, and strong coupling to matter and other fields (such as high-frequency radiation). A proper utilization of these phenomena and effects leads to the new technology of relativistic engineering, in which light-matter interactions in the relativistic regime drives the development of laser-driven accelerator science. A number of significant applications are reviewed, including the fast ignition of an inertially confined fusion target by short-pulsed laser energy and potential sources of energetic particles (electrons, protons, other ions, positrons, pions, etc.). The coupling of an intense laser field to matter also has implications for the study of the highest energies in astrophysics, such as ultrahigh-energy cosmic rays, with energies in excess of ${10}^{20}\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The laser fields can be so intense as to make the accelerating field large enough for general relativistic effects (via the equivalence principle) to be examined in the laboratory. It will also enable one to access the nonlinear regime of quantum electrodynamics, where the effects of radiative damping are no longer negligible. Furthermore, when the fields are close to the Schwinger value, the vacuum can behave like a nonlinear medium in much the same way as ordinary dielectric matter expanded to laser radiation in the early days of laser research.

/pdf/optics-in-the-relativistic-regime-4n43x5jaaf.pdf

Optics in the relativistic regime

As a form of matter intermediate between molecules and bulk solids, atomic clusters have been much studied1 Light-induced processes in clusters can lead to photo-fragmentation2,3 and Coulombic fission4, producing atom and ion fragments with a few electronvolts (eV) of energy However, recent studies of thephotoionization of atomic clusters with high intensity (>1016 W cm−2) femtosecond laser pulses have shown that these interactions can be far more energetic5,6,7,8,9,10,11,12,13—excitation of large atomic clusters can produce a superheated microplasma that ejects ions with kinetic energies up to 1 MeV (ref 10) This phenomenon suggests that through irradiation of deuterium clusters, it would be possible to create plasmas with sufficient average ion energy for substantial nuclear fusion Here we report the observation of nuclear fusion from the explosions of deuterium clusters heated with a compact, high-repetition-rate table-top laser We achieve an efficiency of about 105 fusion neutrons per joule of incident laser energy, which approaches the efficiency of large-scale laser-driven fusion experiments Our results should facilitate a range of fusion experiments using small-scale lasers, and may ultimately lead to the development of a table-top neutron source, which could potentially find wide application in materials studies

Nuclear fusion from explosions of femtosecond laser-heated deuterium clusters

Energy spectra of ions and fast electrons accelerated by a channeling laser pulse in near-critical plasma are studied using three-dimensional (3D) Particle-In-Cell simulations. The realistic 3D geometry of the simulations allows us to obtain not only the shape of the spectra, but also the absolute numbers of accelerated particles. It is shown that ions are accelerated by a collisionless radial expansion of the channel and have nonthermal energy spectra. The electron energy spectra instead are Boltzmann-like. The effective temperature Teff scales as I1/2. The form of electron spectra and Teff depends also on the length of the plasma channel. The major mechanism of electron acceleration in relativistic channels is identified. Electrons make transverse betatron oscillations in the self-generated static electric and magnetic fields. When the betatron frequency coincides with the laser frequency as witnessed by the relativistic electron, a resonance occurs, leading to an effective energy exchange between the l...

Particle acceleration in relativistic laser channels

The generation of extremely bright coherent X-ray pulses in the femtosecond and attosecond regime is currently one of the most exciting frontiers of physics–allowing, for the first time, measurements with unprecedented temporal resolution1,2,3,4,5,6. Harmonics from laser–solid target interactions have been identified as a means of achieving fields as high as the Schwinger limit2,7 (E=1.3×1016 V m−1) and as a highly promising route to high-efficiency attosecond (10−18 s) pulses8 owing to their intrinsically phase-locked nature. The key steps to attain these goals are achieving high conversion efficiencies and a slow decay of harmonic efficiency to high orders by driving harmonic production to the relativistic limit1. Here we present the first experimental demonstration of high harmonic generation in the relativistic limit, obtained on the Vulcan Petawatt laser9. High conversion efficiencies (η>10−6 per harmonic) and bright emission (>1022 photons s−1 mm−2 mrad−2 (0.1% bandwidth)) are observed at wavelengths <4 nm (the `water-window' region of particular interest for bio-microscopy).

/pdf/high-harmonic-generation-in-the-relativistic-limit-3aj6boplxv.pdf

High harmonic generation in the relativistic limit

We report the observation of neutrons rf:leased from d(d,n) He-3 fusion reactions in the focus of 200 mJ, 160 fs Ti:sapphire laser pulses on a deuterated polyethylene target. Optimizing the fast electron and ion generation by applying a well-defined prepulse led to an average rate of 140 neutrons per shot. Furthermore, the production of a substantial number of MeV gamma rays could be observed. The occurrence of neutrons and gamma rays is attributed to the formation and explosion of a relativistic plasma channel in the laser focus, which is confirmed by numerical calculations.

/pdf/neutron-production-by-200-mj-ultrashort-laser-pulses-2brypociso.pdf

Neutron production by 200 mJ ultrashort laser pulses

We present measurements of the samarium $(Z=62)$ $M$-shell absorption band around 11 \AA{} (1.1 keV) at electron temperatures between 5 and 20 eV. Using point projection absorption spectroscopy, we measured the absolute transmission of an x-ray probe beam through a radiatively heated samarium plasma at different drive temperatures. The measurements show two principal absorption features corresponding to the spin-orbit-split $3d\ensuremath{-}4f$ transitions of Sm IV--Sm X ions. The influence of the heating on the spectral opacity shape was characterized by a shift of the absorption features to higher energy for a hotter plasma. The data are compared with calculations done with the superconfiguration code SCO for different plasma temperatures. The temperature and average ionization inferred from the analysis of the experiment are compared to radiative hydrodynamic simulations.

Absorption spectroscopy of a radiatively heated samarium plasma

The absorption of soft X-rays by gold at density of ≈ 0.01 g/cm3 and temperature of ≈ 20 eV has been measured in the photon energy range of 50 to 300 eV. For that purpose, a thin gold foil tamped by carbon was heated by thermal X-rays generated in a laser-irradiated gold cavity and probed by X-rays emitted by a synchronized tungsten backlighter source. The measured absorption was compared with numerical calculations based on the super-transition-array model.

Measurement of the extreme UV opacity of a hot dense gold plasma

We measured in a large spectral range from 180 eV to 20 keV the x-ray emission from aluminum and glass targets irradiated by 150 fs laser pulses at intensities of ≈1017 W/cm2. Unexpected large differences are observed at photon energies above ≈1 keV, where the Al target emitted almost 100 times more x rays than glass. Important for this result is a high prepulse to main pulse contrast.

X-ray emission from metallic (Al) and dielectric (glass) targets irradiated by intense ultrashort laser pulses

Supersonic heat wave in low density foams generated by soft X-radiation from a Z-pinch plasma

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