Source d'électrons femtoseconde

Our goal is to produce ultra-short electron bunches of a few femtoseconds with perfect synchronization to the laser pulse. Such an electron source is unique and would offer new opportunities for applications ranging from ultrafast electron diffraction, femtosecond X-ray generation and radio-biological applications.

 

Laser-plasma accelerator

In practice, we send ultrashort laser pulses into an underdense plasma. The laser pulse excites plasma waves, or wakefields, which in turn can accelerate electrons and produce a femtosecond beam, see figure below.

 

 Figure 1: a) Principle of a laser-plasma accelerator: a femtosecond laser is focused into a gas jet. It ionizes the gas which becomes a plasma. The laser excites a plasma wave which traps and accelerates electrons. b) PIC simulations of a laser (in red) exciting a plasma wave. Electrons, represented in green, form a femtosecond bunch.

A recent highlight of this work is the acceleration of relativistic electrons at kHz, using single-cycle laser pulses.

Recent publications on this subject:

“Relativistic electron beams driven by kHz single-cycle light pulses”; D. Guénot, D. Gustas, A. Vernier, B. Beaurepaire, F. Böhle, M. Bocoum, M. Lozano, A. Jullien, R. Lopez-Martens, A. Lifschitz and J. Faure, submitted (ArXiv 1611.09543)

“Effect of the laser wave front in a laser-plasma accelerator”; B. Beaurepaire, A. Vernier, M. Bocoum, F. Böhle, A. Jullien, J.-P. Rousseau, T. Lefrou, D. Douillet, G. Iaquaniello, R. Lopez-Martens, A. Lifschitz and J. Faure; Phys. Rev. X 5 031012 (2015)

“Electron acceleration in sub-relativistic wakefields driven by few-cycle laser pulses”; B. Beaurepaire, A. Lifschitz and J. Faure, New J. Physics 16023023 (2014)

 

Application to ultrafast electron diffraction

We have recently used these electron beams generated from plasmas to perform electron diffraction experiments and even time-resolved diffraction. Typical diffraction patterns are shown in the figure below. The peaks, called Bragg peak, are due to the diffraction of electron wave packets on the crystal lattice of a gold nano-membrane.

Figure 2: left: diffraction pattern from a gold nano-membrane obtained using our laser-plasma source. For comparison, we show the diffraction pattern obtained with the same sample but using a conventional DC electron gun, developed in our laboratory.


 Recent publications on this subject:

“Capturing structural dynamics in crystalline silicone using chirped electrons from a laser wakefield accelerator”; Z. He, B. Beaurepaire, J.A. Nees, G. Gallé, S.A. Scott,  J.R. Sanchez Pérez, M.G. Lagally, K. Krushelnick, A.G.R. Thomas and J. Faure, Sci. Rep. 6, 36224 (2016). DOI: 10.1038/srep36224

“Concept of a laser-plasma-based electron source for sub-10-fs electron diffraction”; J. Faure, B. van der Geer, B. Beaurepaire, G. Gallé, A. Vernier and A. Lifschitz; Phys. Rev. Acc. and Beams 19, 021302 (2016)

“Electron diffraction using ultrafast electron bunches from a laser wakefield accelerator at KHz repetition rate”, Z.-H. He, A. G. R. Thomas, B. Beaurepaire, J. A. Nees, B. Hou, V. Malka, K. Krushelnick and J. Faure, Appl. Phys. Lett. 102, 064104 (2013)

 

Interaction with solid targets

We are also investigating the possibility to use the interaction of a femtosecond laser pulse with a solid target for generating electrons. At the moment, we are mostly concerned about unraveling the fundamental physics of the acceleration process. The image below shows the reflexion of an ultra-intense laser field onto a solid target. Electrons are accelerated a4 eacH oqtical cycle and are ejected toward the vacuum.

 


Figure 3: PIC simulations of an ultra-intense laser field reflexion on a solid target. The magnetic field is represented in false color. Electrons are represented a black dots. Electrons are pulled away from the solid surface by the laser and ejected toward the vacuum.

 Recent publications on this subject:

“On the physics of electron ejection from laser-irradiated overdense plasmas”, M. Thévenet, H. Vincenti and J. Faure; Phys. Plasmas 23, 063119 (2016)

“Anticorrelated emission of high harmonics and fast electron beams from plasma mirrors”; Maïmouna Bocoum, Maxence Thévenet, Frederik Böhle, Benoît Beaurepaire, Aline Vernier, Aurélie Jullien, Jérôme Faure, and Rodrigo Lopez-Martens ; Phys. Rev. Lett. 116, 185001 (2016)

“Vacuum laser acceleration of relativistic electrons using plasma mirror injectors”; M. Thévenet, A. Leblanc, S. Kahaly, H. Vincenti, A. Vernier, F. Quéré and J. Faure; Nature Physics 12, 355 (2016)


Contact

For more information, contact Jérôme FAURE, jerome.faure@ensta.fr

 

ENSTA CNRS Ecole Polytechnique