Imaging of Plasmas Using Proton Beams Generated by Ultra-Intense Laser Pulses

摘要

During the interaction of ultraintense laser pulses with plasmas and solid targets, a considerable fraction of the laser energy is deposited into highly energetic charged particles. One of the most exciting results recently obtained in this area of research is the observation of very energetic beams of protons, generated during the interaction of ultraintense short pulses with solid targets. In a number of experiments, performed with different laser systems and in different interaction conditions, protons with energies up to several tens of MeV have been detected behind thin foils irradiated with high intensity pulses. In these experiments it was seen that the particle beams are directed along the normal to the back surface of the target, and have a small angular aperture at the highest energies. As proton beams are observed even using target which nominally do not contain hydrogen, protons are thought to originate from hydro-carbon impurities located on the target surfaces or from bulk contamination of the target. Proposed theoretical models indicate that the protons gain their energy from the enormous electric field (-MV/micron) set up laser accelerated fast electrons via space-charge at the back target surface. As protons are easier to accelerate than heavier ions, protons are the dominant component of the ion emission.