Abstract
We present a method for the generation of high kinetic energy attosecond electron packets via magnetostatic and aperture filtering of conical surface plasmon (SP) accelerated electrons. The conical SP waves are excited by coupling an ultrafast radially polarized laser beam to a conical silica lens coated with an Ag film. Electromagnetic and particle tracking models are employed to characterize the ultrafast electron packets.
Highlights
To ensure that the findings are generalizable to a realistic situation, the Ag film is modelled to have a surface roughness of 2.8 nm rms (Ref. 25) such that the influence of enhanced surface plasmon (SP) fields localized at random spots is captured
Second, electrons are generated by placing them randomly along the vacuum side of the Ag film. These electrons are subsequently tracked in time and space as they interact with the ESP field through the nonrelativistic equation of motion
The poor performance of the linearly polarized configuration can be directly attributed to the laser pulse only coupling to an SP wave in one plane (i.e. the xz plane at the center of the conical lens in Fig. 1(a)), leading to a reduction in the electric field enhancement occurring at the apex of the conical lens
Summary
The use of a radially polarized beam affords the benefit of having the electric field polarization oriented such that it is p-polarized with respect to the Ag film along the entire azimuthal angle of the conical lens This leads to the excitation of traveling SP waves encompassing the entire conical surface of the Ag film, a so-called conical SP wave. Throughout the calculations, the peak intensity of the optical pulse is kept below 1.2 × 1012 W/cm[2] which is below the experimentally determined damage threshold of a thin Ag film on a silica prism[25] At this intensity, and with a spot size diameter of ~6 μ m for a radially polarized beam, the corresponding energy per laser pulse is calculated to be ~1 nJ. As this value is well below 107 electrons/packet, space charge effects will not be encountered[25]
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