It has been found that more intense proton beams are generated from plastic foils than metal foils irradiated by an ultraintense
laser pulse. The acceleration model, ARIE (Acceleration by a Resistively Induced Electric field) accounts for the
experimental observations from plastic foils compared with metal foils. Proton beams on foil thickness and laser prepulse
have been observed, which is also well described by the ARIE model. An experiment with an aluminum-coated
plastic target strongly suggests that front side acceleration is a dominant acceleration process in plastic targets. We also
suggest that a vacuum-sandwiched double layer target could effectively enhance the laser contrast ratio, which was
investigated in the combination of a two-dimensional hydro code and a two-dimensional PIC (Particle-In-Cell) code.
A compact gamma-ray source using laser-accelerated electron beam is being under development at KAERI for nuclear
applications, such as, radiography, nuclear activation, photonuclear reaction, and so on. One of two different schemes,
Bremsstrahlung radiation and Compton backscattering, may be selected depending on the required specification of
photons and/or the energy of electron beams. Compton backscattered gamma-ray source is tunable and quasimonochromatic
and requires electron beams with its energy of higher than 100 MeV to produced MeV photons.
Bremsstrahlung radiation can generate high energy photons with 20 - 30 MeV electron beams, but its spectrum is
continuous. As we know, laser accelerators are good for compact size due to localized shielding at the expense of low
average flux, while linear RF accelerators are good for high average flux. We present the design issues for a compact
gamma-ray source at KAERI, via either Bremsstrahlung radiation or Compton backscattering, using laser accelerated
electron beams for the potential nuclear applications.
High-repetition-rate, femtosecond x-ray lasers would be useful for dynamical study of ultra-fast phenomena in nature. One of routes to get fs x-ray lasers is to use inner-shell processes in atomic and ionic systems. In this paper, the two inner-shell schemes recently proposed will be reviewed and compared in detail. One of important issues using inner-shell schemes is fast and intense x-ray pumping source. One of good candidate sources for that purpose is Larmor radiation produced by electrons under an intense fs laser field. The relativistic, nonlinear Thomson scattering by an electron of an intense laser field is investigated in computer simulation. Under a laser field with a pulse duration of 20 fs Full Width Half Maximum and an intensity of 1020 W/cm2, the motion of an electron is highly relativistic and generates an ultra-short radiation of 2 attoseconds with photon energies of 100 to 600 eV. An interesting modulated structure of the spectrum is observed and analyzed. A radiation produced by the zigzag motion of an electron under a linearly polarized laser has better characteristics than by a helical motion under a circularly polarized laser pulse in terms of an angular divergence and an energy spectrum.