Particle acceleration based on high intensity laser systems (a process known as laser-plasma acceleration) has achieved high quality particle beams that compare favourably with conventional acceleration techniques in terms of emittance, brightness and pulse duration. A long-term difficulty associated with laser-plasma acceleration--the very broad, exponential energy spectrum of the emitted particles--has been overcome recently for electron beams. Here we report analogous results for ions, specifically the production of quasi-monoenergetic proton beams using laser-plasma accelerators. Reliable and reproducible laser-accelerated ion beams were achieved by intense laser irradiation of solid microstructured targets. This proof-of-principle experiment serves to illuminate the role of laser-generated plasmas as feasible particle sources. Scalability studies show that, owing to their compact size and reasonable cost, such table-top laser systems with high repetition rates could contribute to the development of new generations of particle injectors that may be suitable for medical proton therapy.

We report the observation of subpicosecond terahertz (T-ray) pulses with energies ≥460 μJ from a laser-driven ion accelerator, thus rendering the peak power of the source higher even than that of state-of-the-art synchrotrons. Experiments were performed with intense laser pulses (up to 5×10(19) W/cm(2)) to irradiate thin metal foil targets. Ion spectra measured simultaneously showed a square law dependence of the T-ray yield on particle number. Two-dimensional particle-in-cell simulations show the presence of transient currents at the target rear surface which could be responsible for the strong T-ray emission.

Nuclear-resonance-fluorescence spectra have been measured in the chain of l48l50 ' 152154 Sm isotopes. Together with supplementary information from inelastic electron scattering and other reaction studies, orbital Ml transition strengths have been deduced from a number of 1 + states located around an excitation energy of 3 MeV. The systematic study, carried out for the first time, for nuclei within a large range of the deformation parameter 8 shows that the orbital Ml strength varies quadratically with 8. This result is interpreted in terms of models containing explicitly neutron and proton degrees of freedom.PACS numbers: 21.10. Re, 23.20.Qz, 25.20.Dc, 27.70.+q The role of neutron-proton interactions on collective nuclear excitations has been a subject of investigations for over four decades. Soon after the discovery of giant dipole resonances, they were interpreted 1 as isovector volume vibrations with neutrons as a whole oscillating out of phase against protons. More recently, a so-called "scissors mode" of oscillations based on a macroscopic two-rotor model (TRM) was suggested, 2 which predicts that 1 + levels with strong ground-state Ml transitions occur in even-even deformed nuclei. The discovery 3 of A/1 excitations in heavy deformed nuclei by highresolution inelastic electron scattering led to a series of detailed investigations on experimental and theoretical fronts. 4 These excitations today still constitute also the best proof for the so-called "mixed-symmetry states" in the neutron-proton interacting-boson model (IBM-2). 5 Macroscopic calculations predict that the orbital Ml strength is to be found in one or a few states, while the experiments indicate that it is generally fragmented into more levels (see, e.g., Refs. 4 and 6). This disparity with macroscopic descriptions is attributed to two-quasiparticle excitations. 7 Very recently, a systematic study 8 of Ml strength in the rare-earth region within the Nilsson model has shown quantitatively a direct correlation between the quadrupole ground-state deformation and the orbital magnetic dipole strength. This finding is also in agreement with predictions 5,9 of the interacting-boson model where in both the SU(3) and the 0(6) limits, i.e., the case where nonspherical nuclei rotate and vibrate, respectively, the reduced Ml transition strength is proportional to N X NJ(N X +N V ), with N K (N v ) being the number of valence proton (neutron) bosons, and is thus within a given series of isotopes not only a function of the number of neutrons present but predominantly dependent upon the neutron-proton interaction responsible for the quadrupole deformation of nuclear ground states. 10 Besides these two classes of models, other calculations exist where the deformation parameter 5 is explicitly contained in the analytic expressions for the reduced Ml transition strength. Some of them are random-phase-approximation predictions; 11 " 13 others re-sult from the TRM, sum-rule, and so-called giantangle-dipole approaches. 14 " 16 These predictions, which are listed...

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