Theoretical Investigation of Controlled Generation of a Dense Attosecond Relativistic Electron Bunch from the Interaction of an Ultrashort Laser Pulse with a Nanofilm

Abstract

For controllable generation of an isolated attosecond relativistic electron bunch [relativistic electron mirror (REM)] with nearly solid-state density, we propose using a solid nanofilm illuminated normally by an ultraintense femtosecond laser pulse having a sharp rising edge. With two-dimensional (2D) particlein-cell (PIC) simulations, we show that, in spite of Coulomb forces, all of the electrons in the laser spot can be accelerated synchronously, and the REM keeps its surface charge density during evolution. We also developed a self-consistent 1D theory, which takes into account Coulomb forces, radiation of the electrons, and laser amplitude depletion. This theory allows us to predict the REM parameters and shows a good agreement with the 2D PIC simulations. Generation of attosecond relativistic electron beams is of great importance for modern physics. These beams can be used in modern laser-wakefield accelerators and freeelectron lasers for injection, in attosecond electron diffraction and microscopy, in generation of ultrashort coherent xray radiation via Thomson scattering, and in many other applications, providing time-resolved studies in physics, biology, chemistry, etc., with the attosecond time-scale resolution. The main requirement for attosecond electron bunches is the controllability of their parameters, including length, charge, and energy.In high-density (overcritical) plasmas, two mechanisms for generation of ultrashort electron beams -the v B heating and the vacuum heating -were investigated recently [1][2][3][4]. The length of the electron beam is about the laser pulse length here with a wide energy spread for electrons; in addition, the beam parameters are difficult to control. In low-density (underdense) plasmas, a single electron bunch can be generated by laser-wakefield acceleration mechanism [5][6][7] but the length of the bunch is not shorter than 1-5 m (several femtoseconds). In a vacuum, a single ultrashort electron beam can be generated through laser compression of a longer electron beam [8,9]; however, the charge of the bunch here is considerably smaller than 1 pC. The same compression can be applied for thin (1 m and less) plasma layers of low (gas) density [10 -12], but the practical realization of such layers is under question now.In this Letter, we propose using a nanofilm (film with a thickness of 10 nm or less) as a solid-state density target for generation of an attosecond relativistic electron bunch. It is shown that, when this target is irradiated normally by a superhigh intensity laser pulse with a sharp rising edge (nonadiabatic laser pulse), all electrons of the plasma layer can achieve relativistic longitudinal velocities synchronously when the dimensionless field amplitude becomes large enough, a 0 [a 0 jejE 0 = mc! ,, where e and m are the charge and the mass of an electron, c is the speed of light, E 0 , !, and are the amplitude, the frequency, and the wavelength of the laser field in a vacuum, ! p 4 n 0 e 2 =m p is the characteristic plasma frequency, n 0 and l are th...

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