No abstract

No abstract

We present experimental studies on ion acceleration using an 800-nm circularly polarized laser pulse with a peak intensity of 6.9×10^{19}  W/cm^{2} interacting with an overdense plasma that is produced by a laser prepulse ionizing an initially ultrathin plastic foil. The proton spectra exhibit spectral peaks at energies up to 9 MeV with energy spreads of 30% and fluxes as high as 3×10^{12}  protons/MeV/sr. Two-dimensional particle-in-cell simulations reveal that collisionless shocks are efficiently launched by circularly polarized lasers in exploded plasmas, resulting in the acceleration of quasimonoenergetic proton beams. Furthermore, this scheme predicts the generation of quasimonoenergetic proton beams with peak energies of approximately 150 MeV using current laser technology, representing a significant step toward applications such as proton therapy.

A pulse cleaner based on noncollinear optical-parametric amplification and second-harmonic generation processes is used to improve the contrast of a laser of peak intensity ∼2 × 1019 W/cm2 to ∼1011 at 100 ps before the peak of the main pulse. A 7 MeV proton beam is observed when a 2.5 μm-thick Al foil is irradiated by this high-contrast laser. The maximum proton energy decreases to 2.9 MeV when a low-contrast (∼108) laser is used. Two-dimensional particle-in-cell simulations combined with MULTI simulations show that the maximum proton energy sensitively relies on the detecting direction. The ns-time-scale prepulse can bend a thin target before the main pulse arrives, which reduces maximum proton energy in the target normal sheath acceleration.

We present experimental studies on ion acceleration from diamond-like carbon (DLC) foils irradiated by 800 nm, linearly polarized laser pulses with peak intensity of 1.7 Â 10 19 W/cm 2 to 3.5 Â 10 19 W/cm 2 at oblique incidence. Diamond-like carbon foils are heated by the prepulse of a high-contrast laser pulse and expand to form plasmas of near-critical density caused by thermal effect before the arrival of the main pulse. It is demonstrated that carbon ions are accelerated by a collisionless shock wave in slightly overdense plasma excited by forward-moving hot electrons generated by the main pulse. V C 2015 AIP Publishing LLC. [http://dx.

A double beam image (DBI) technique is coupled in the two-stage accelerating mechanism to simultaneously improve the spectra and maximum energy of the proton beam. A proton beam with a narrow-spectrum center at 5.4 MeV and a long tail up to 14.4 MeV is generated in the experiment. Experimental and simulation results show that spatial collineation, time synchronization, and real-time monitoring are needed for optimum two-stage proton acceleration and are realized by the DBI technique to a certain extent in our experiment. This DBI technique can be used to achieve optimum two-stage acceleration in a feasible manner and will allow precise manipulation of multistage acceleration to improve the energy and spectra of particle beams.

The accelerating gradient of a proton beam is a crucial factor for the stable radiation pressure acceleration, because quickly accelerating protons into the relativistic region may reduce the multidimensional instability grow to a certain extent. In this letter, a shape-tailored laser is designed to accelerate the protons in a controllable high accelerating gradient in theory. Finally, a proton beam in the gigaelectronvolt range with an energy spread of ∼2.4% is obtained in one-dimensional particle-in-cell simulations. With the future development of the high-intense laser, the ability to accelerate a high energy proton beam using a shape-tailored laser will be important for realistic proton applications, such as fast ignition for inertial confinement fusion, medical therapy, and proton imaging.

Lower charge-to-mass ions are more difficult to be accelerated during the traditional single accelerating progress, because they are generally modulated by the weaker charge-separated electric field. In this paper, the cascaded target normal sheath acceleration (TNSA) mechanism is proposed to solve this issue in experiments, where the low charge-to-mass ions (C2+) generated from the first TNSA stage can be further tailored to a mono-energetic bunch by the peak of the sheath field in the additive TNSA stages. A simple numerical model is used to explain the experimental result and shows that the energetic spread of the ion beam can be further reduced from 27% to ∼1% by expanding the two-stage acceleration to triple-stage acceleration. Here, the sheath field works like a spectral knife that can control the peak energy and bandwidth of the spectra for the ions with any charge-to-mass ratio. More choices can be provided for many potential applications, such as ion therapy and nuclear physics.