Laser Ion Acceleration from the Interaction of Ultra-Intense Laser Pulse with Thi Foils

Download or read book Laser Ion Acceleration from the Interaction of Ultra-Intense Laser Pulse with Thi Foils written by and published by . This book was released on 2004 with total page 179 pages. Available in PDF, EPUB and Kindle. Book excerpt: The discovery that ultra-intense laser pulses (I> 1018 W/cm2) can produce short pulse, high energy proton beams has renewed interest in the fundamental mechanisms that govern particle acceleration from laser-solid interactions. Experiments have shown that protons present as hydrocarbon contaminants on laser targets can be accelerated up to energies> 50 MeV. Different theoretical models that explain the observed results have been proposed. One model describes a front-surface acceleration mechanism based on the ponderomotive potential of the laser pulse. At high intensities (I> 1018 W/cm2), the quiver energy of an electron oscillating in the electric field of the laser pulse exceeds the electron rest mass, requiring the consideration of relativistic effects. The relativistically correct ponderomotive potential is given by Up = ([1 + I[lambda]2/1.3 x 1018]1/2 - 1) moc2, where I[lambda]2 is the irradiance in W[mu]m2/cm2 and moc2 is the electron rest mass. At laser irradiance of I[lambda]2 ~ 1018 W[mu]m2/cm2, the ponderomotive potential can be of order several MeV. A few recent experiments--discussed in Chapter 3 of this thesis--consider this ponderomotive potential sufficiently strong to accelerate protons from the front surface of the target to energies up to tens of MeV. Another model, known as Target Normal Sheath Acceleration (TNSA), describes the mechanism as an electrostatic sheath on the back surface of the laser target. According to the TNSA model, relativistic hot electrons created at the laser-solid interaction penetrate the foil where a few escape to infinity. The remaining hot electrons are retained by the target potential and establish an electrostatic sheath on the back surface of the target.