Laser particle acceleration at relativistic laser intensity

Abstract

Laser-driven particle acceleration has been investigated using a 30 fs, PW laser. By applying circularly polarized laser pulses at an intensity of 6x10 W/cm, 80-MeV protons were produced. Keywords; energetic proton generation; radiation pressure acceleration; PW laser; The research on laser-matter interactions has entered a new era in the relativistic regime thanks to the recent rapid progress of ultrashort high-power laser technologies. High-power femtosecond lasers, reaching an output power over 1 PW, have been built or being developed in a number of institutes around the world. At Gwangju Institute of Science and Technology (GIST) two PW Ti:Sapphire laser beamlines have been developed, achieving outputs of 1.0 PW and 1.5 PW at 30 fs [1,2]. Using this PW laser facility, the Center for Relativistic Laser Science (CoReLS), a research center of Institute for Basic Science (IBS), works on experimental and theoretical investigations of relativistic laser-matter interactions. We explore the physical processes of laser – matter interactions at relativistic laser intensities. The interactions between ultra-intense laser pulses and matter can create extreme physical conditions. The typical physical parameters – electric and magnetic fields, temperature, pressure and acceleration – accessed with ultra-intense laser pulses can easily exceed those obtained with conventional methods by many orders of magnitude. Ultra-intense laser pulses, as the primary source, or short-wavelength radiation and energetic charged particles, as the secondary source, can expose matter under extreme conditions. The exploration of such extreme physical conditions would bring out novel consequences in fundamental physics of laser-matter interactions. A series of experiments have been performed using the 100 TW and PW lasers at GIST. Using the laser with 100 TW output some experiments, such as stable laser electron acceleration [3] and relativistic high-harmonic generation from solid targets [4], have been carried out. Using the PW laser output we succeeded in generating multi-GeV electrons through two stages of amplification [5] and in producing protons with energy of 45 MeV [6]. We have made intense efforts to produce protons in the 100 MeV range. The result in [6] was obtained by applying linearly polarized PW laser pulses. For further improvement we applied circularly polarized PW laser pulses at an intensity of 6x10 W/cm on ultrathin targets, obtaining 80 MeV protons due mainly to radiation pressure acceleration. Applications of these particle and radiation beams with unique characteristics will open up new research areas, such as material characterization at extreme conditions, ultrafast imaging of atoms, molecules and nano-structures, exploration of astrophysical events, and even hadron oncology.