Acceleration of heavy multicharged ions in the interaction of a subrelativistic femtosecond laser pulse with a melted me
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LE ACCELERATION IN PLASMA
Acceleration of Heavy Multicharged Ions in the Interaction of a Subrelativistic Femtosecond Laser Pulse with a Melted Metal Surface K. A. Ivanov, D. S. Uryupina, N. Morshedian, R. V. Volkov, and A. B. Savel’ev Faculty of Physics and International Laser Center, Lomonosov Moscow State University, Moscow, 119991 Russia Received June 4, 2009
Abstract—Results are presented from experimental studies of ion acceleration under the action of femtosec ond laser pulses with an intensity of 1017 W/cm2, incident onto the free surfaces of melted gallium and indium. The effect of the polarization direction of a linearly polarized laser pulse and the amplitude of a short prepulse, which precedes the main pulse by several nanoseconds, on the parameters of accelerated ions is investigated. It is found that, even for such a moderate laser intensity, the characteristic velocity of fast ions ejected along the reflected beam is a factor of 1.5 higher than that of ions ejected along the normal to the target surface. It is shown that, as the prepulse energy increases, the hard Xray yield and the mean energy of hot electrons increase substantially, whereas the velocity of both fast and slow ions decreases appreciably regard less of laser polarization. DOI: 10.1134/S1063780X10020017
trast laser radiation with a short prepulse or long ped estal [6–9]. As was mentioned above, the energy and direc tional pattern of accelerated ions are determined by the parameters of electrons emitted from the plasma. The efficiency of ion acceleration also depends on the ion composition of the target. Thus, in a plasma pro duced on a solid target surface, light impurity ions that are usually present on the target surface are mainly accelerated [10–12].This hinders efficient ionization and acceleration of ions of the main target material. It was found in [10–12] that the acceleration efficiency of ions of the main target material increased substan tially when the target surface was preheated or pre cleaned by a laser pulse. It was also shown that, by varying the density of light ions on the target surface, it was possible to obtain quasimonoenergetic beams of light ions [10–12]. When a cell filled with a melted metal is used as a target, the target surface is restored automatically after the action of the laser pulse. In this case, it is unneces sary to refresh or shift the target surface before the next laser pulse [7–9]. Moreover, when metal is heated to above 100°С, light molecules of water and carbohy drates adsorbed on the surface are removed, due to which the acceleration efficiency of metal ions increases substantially. In this paper, we study acceleration of heavy multi charged ions under the action of femtosecond laser pulses with an intensity of 1017 W/cm2, incident onto the free surfaces of melted gallium and indium. The effect of the polarization direction of a linearly polar
1. INTRODUCTION Plasma produced by an intense femtosecond laser pulse is an efficient source of incoherent hard Xray (HXR) emission,
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