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Two-dimensional phase shaping for electron acceleration

English title Two-dimensional phase shaping for electron acceleration
Applicant Lüthy Willy
Number 126553
Funding scheme Project funding (Div. I-III)
Research institution Institut für angewandte Physik Universität Bern
Institution of higher education University of Berne - BE
Main discipline Technical Physics
Start/End 01.01.2010 - 31.03.2011
Approved amount 87'830.00
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All Disciplines (2)

Discipline
Technical Physics
Other disciplines of Physics

Keywords (5)

thermal dispersion; phase shaping; electron acceleration; Thermo-optical phase modulation; femtosecond pulse shaping

Lay Summary (English)

Lead
Lay summary
Vacuum acceleration of charged particles is a challenging task since it is difficult to accelerate particles when the field direction and the propagation direction of the light are perpendicular to each other and when and since it is not easy to match the velocity of the light pulse to the velocity of the particle. Here, we propose a new scheme which - at least in concept - has a number of advantages over existing proposals. This scheme is based on spatiotemporal pulse shaping of ultrafast optical light pulses.A free electron in the electromagnetic field of a light field is influenced by the electric and the magnetic fields due to the Lorentz force. The magnetic field becomes important only for large electron velocities. For an electron initially at rest the electric field leads to acceleration during one half wave. During the following half wave the electric field has changed its direction and the electron is decelerated to rest again. To reach high electron energy, the phase of the electromagnetic field has to be modified so that the electron remains in a field of constant direction over a longer time. Ideally the electron should surf on the peak of the electric field. Therefore, the electromagnetic field has to be tailored such that everywhere along its trajectory the electron experiences the same maximum field strength and direction, even in the regime where the magnetic component of the light field plays an important role in the electron dynamics.Recently, we have shown that an adaptive mirror based on thermal dispersion is well suited to modify the phase of a laser beam. This adaptive mirror is simple and robust; most importantly it can withstand high laser intensities. The desired two-dimensional phase distribution is generated by selectively heating the adaptive mirror with the emission of a video projector. Such adaptive mirrors have proved to be a versatile tool for a number of different applications. In the present project we will first calculate the required phase distribution. Based on this modelling the phase distribution will experimentally be realised with an intense femtosecond laser pulse. The phase in the focal region will be measured before starting the experiments for electron acceleration.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

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Associated projects

Number Title Start Funding scheme
117609 Thermo-optical phase modulator for femtosecond pulse management 01.01.2008 Project funding (Div. I-III)
117609 Thermo-optical phase modulator for femtosecond pulse management 01.01.2008 Project funding (Div. I-III)

Abstract

A free electron in an electromagnetic field is influenced by the electric and the magnetic fields due to the Lorentz force. The magnetic field becomes important only for large electron velocities. For an electron initially at rest the electric field, however, leads to acceleration during one half wave. During the following half wave the electric field has changed its direction and the electron is decelerated to rest again. To reach higher electron energy, the phase of the electromagnetic field has to be modified so that the electron over a long time remains in a field of constant direction. Most efficiently the electron should surf on the peak of the electric field. Therefore the field has to be shaped such that everywhere along its trajectory the electron experiences the same maximum field strength and direction, even in the regime where the magnetic component of light plays an important role in the electron dynamics. We have shown before, that an adaptive mirror based on thermal dispersion is well suited to modify the phase of a laser beam. This adaptive mirror is simple and robust; it can withstand high laser intensities. The desired two-dimensional phase distribution is generated by selectively heating the adaptive mirror with the emission of a video projector. Such adaptive mirrors have proved to be a versatile tool for a number of different applications (see 2.2.1.). In the present project we will first calculate the required phase distribution. Based on this modelling the phase distribution will experimentally be realised with an intense femtosecond laser. The phase in the focal region will be measured before starting the experiments for electron acceleration. The experiments with high energy electrons will be performed in collaboration with the Paul Scherrer Institute (PSI).
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