Abstract
A scheme to obtain brilliant x-ray sources by coherent reflection of a counter-propagating pulse from laser-driven dense electron sheets is theoretically and numerically investigated in a self-consistent manner. A radiation pressure acceleration model for the dynamics of the electron sheets blown out from laser-irradiated ultrathin foils is developed and verified by PIC simulations. The first multidimensional and integral demonstration of the scheme by 2D PIC simulations is presented. It is found that the reflected pulse undergoes Doppler-upshift by a factor 4γz2, where γz=(1- vz2/c2)-1/2 is the effective Lorentz factor of the electron sheet along its normal direction. Meanwhile the pulse electric field is intensified by a factor depending on the electron density of the sheet in its moving frame ne/γ, where γ is the full Lorentz factor.
Highlights
In order to blow out all foil electrons, the laser ponderomotive force (v/c) × BL ∼ EL has to be larger than the maximum electrostatic field Es,max = 4π en0l0 induced due to the charge separation
Due to the strong radiation pressure, all foil electrons are quickly blown out, forming a dense electron sheet co-moving with the laser pulse
Figure 1. 1D PIC simulation results: electron density ne/nc, laser field Ex, and charge separation field Ez at t = 4T (T = 2π/ω), zoomed in inset, for foil with initial density n0 = 200nc and thickness l0 = 5 nm irradiated by x-polarized laser at amplitude a0 = 60 and wavelength λ = 1 μm
Summary
In order to blow out all foil electrons, the laser ponderomotive force (v/c) × BL ∼ EL has to be larger than the maximum electrostatic field Es,max = 4π en0l0 induced due to the charge separation. This means that the foil thickness l0 should satisfy l0 λ. 1D PIC simulation results: electron density ne/nc (black), laser field Ex (blue), and charge separation field Ez (red) at t = 4T (T = 2π/ω), zoomed in inset, for foil with initial density n0 = 200nc and thickness l0 = 5 nm irradiated by x-polarized laser at amplitude a0 = 60 and wavelength λ = 1 μm. In the scheme for coherent production of x-ray sources that we discuss, the dense electron sheet acts, within its life time, as a stable relativistic mirror
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