Abstract
We report on a theoretical and experimental study of the energy transfer between an optical evanescent wave, propagating in vacuum along the planar boundary of a dielectric material, and a beam of sub-relativistic electrons. The evanescent wave is excited via total internal reflection in the dielectric by an infrared (λ = 2 μm) femtosecond laser pulse. By matching the electron propagation velocity to the phase velocity of the evanescent wave, energy modulation of the electron beam is achieved. A maximum energy gain of 800 eV is observed, corresponding to the absorption of more than 1000 photons by one electron. The maximum observed acceleration gradient is 19 ± 2 MeV/m. The striking advantage of this scheme is that a structuring of the acceleration element's surface is not required, enabling the use of materials with high laser damage thresholds that are difficult to nano-structure, such as SiC, Al2O3 or CaF2.
Highlights
The study of the interaction between photons and free charged particles began shortly after the invention of the laser, motivated by the goal to accelerate particles with the large fields generated by focused laser light
In this paper we propose and experimentally demonstrate an alternative approach using the interaction of free electrons with an evanescent wave excited on the planar surface of a dielectric material by total internal reflection
In the experimental part we show the results of a proof-ofprinciple experiment demonstrating the acceleration of electrons by an optical evanescent wave generated at a non-structured surface using a sub-relativistic electron beam
Summary
The study of the interaction between photons and free charged particles began shortly after the invention of the laser, motivated by the goal to accelerate particles with the large fields generated by focused laser light. In the laserwakefield acceleration scheme [1,2], high-energy femtosecond laser pulses are used to drive a wake wave in a plasma. Particles can be trapped in such a wave and accelerated to energies of several GeV [3,4,5]. Another example is the so-called inverse free-electron laser [6,7], where the electrons are accelerated via interaction with laser fields inside the periodic magnetic fields of an undulator. Laser acceleration is possible using high-intensity laser pulses focused into a near-critical plasma [8]
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