attosecond relativistic electron control
The ultra-strong fields of intense laser pulses can drive electrons to the speed of light and steer these relativistic electrons on nano- to micrometer length scales and attosecond time scales.
Consider, for example, the few-femtosecond relativistic electron bunch emerging from a laser-driven plasma accelerator
crossing two counter-propagating focused beams of a few-cycle laser pulse. Within the half cycle when the pulses’ combined electric field points forward, it boosts the electrons’ energy, during the next half cycle the force is reversed and brakes the electrons. In this way the electron energy is modulated by the oscillating laser field on an attosecond time scale. If this is performed with a few-cycle laser wave, there may be only one half cycle, which boosts the electron energy to the highest value, hence filtering of the electrons within this energy band in a subsequent “chicane” (which deflects electrons with different energies differently) may lead to an attosecond (in this example: 500 as) electron bunch.
crossing two counter-propagating focused beams of a few-cycle laser pulse. Within the half cycle when the pulses’ combined electric field points forward, it boosts the electrons’ energy, during the next half cycle the force is reversed and brakes the electrons. In this way the electron energy is modulated by the oscillating laser field on an attosecond time scale. If this is performed with a few-cycle laser wave, there may be only one half cycle, which boosts the electron energy to the highest value, hence filtering of the electrons within this energy band in a subsequent “chicane” (which deflects electrons with different energies differently) may lead to an attosecond (in this example: 500 as) electron bunch.
Fig. 1. A strong laser pulse strips a bunch of electrons from a thin foil.
Another example for relativistic attosecond control is shown in Fig. 1. The electric and magnetic force of an ultra-intense few-cycle laser pulse accelerates electrons within a tiny fraction of the wave period, i.e. within several hundred attoseconds, to the speed of light and push them forward, tearing them away from a thin nanometre foil as a thin layer. This layer may contain some 10 billion electrons, packed as densely as inside a solid. This ultra-dense “electron layer” flies with nearly the speed of light as is obvious from Fig. 1 showing the electron bunch riding the accelerating electric wave cycle. The same laser wave can drive relativistic electron density oscillations at the surface of a thick target, upon impinging on it.
These examples demonstrate how ultra-strong few-cycle light fields with controlled waveform may, one day, allow the control of the relativistic motion of electrons at high densities. This control, in turn, will open the door for the development of attosecond and ultrabrilliant sources of X-rays.
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