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Michel Piché

Publications and source records attributed to Michel Piché.

7 recordsLinked to original sources
arXiv2024

Relativistic electrons from vacuum laser acceleration using tightly focused radially polarized beams

We generate a tabletop pulsed relativistic electron beam at 100 Hz repetition rate from vacuum laser acceleration (VLA) by tightly focusing a radially polarized beam into a low-density gas. We demonstrate that strong longitudinal electric fields at the focus can accelerate electrons up to 1.43 MeV by using only 98 GW of peak laser power. The electron energy is measured as a function of laser intensity and gas species, revealing a strong dependence on the atomic ionization dynamics. These experimental results are supported by numerical simulations of particle dynamics in a tightly focused configuration that take ionization into consideration. For the range of intensities considered, it is demonstrated that atoms with higher atomic numbers like krypton can optimally inject electrons at the peak of the laser field, resulting in higher energies and an efficient acceleration mechanism that reaches a significant fraction of the theoretical energy gain limit.

physics.optics↗
arXiv2015

MeV femtosecond electron pulses from direct-field acceleration in low density atomic gases

Using three-dimensional particle-in-cell simulations, we show that few-MeV electrons can be produced by focusing tightly few-cycle radially-polarized laser pulses in a low-density atomic gas. In particular, it is observed that for the few-TW laser power needed to reach relativistic electron energies, longitudinal attosecond microbunching occurs naturally, resulting in femtosecond structures with high-contrast attosecond density modulations. The three-dimensional particle-in-cell simulations show that in the relativistic regime the leading pulse of these attosecond substructures survives to propagation over extended distances, suggesting that it could be delivered to a distant target, with the help of a properly designed transport beamline.

physics.optics↗
arXiv2013

Femtosecond 240-keV electron pulses from direct laser acceleration in a low-density gas

We propose a simple laser-driven electron acceleration scheme based on tightly focused radially polarized laser pulses for the production of femtosecond electron bunches with energies in the few-hundreds-of-keV range. In this method, the electrons are accelerated forward in the focal volume by the longitudinal electric field component of the laser pulse. Three-dimensional test-particle and particle-in-cell simulations reveal the feasibility of generating well-collimated electron bunches with an energy spread of 5% and a temporal duration of the order of 1 fs. These results offer a route towards unprecedented time resolution in ultrafast electron diffraction experiments.

physics.acc-ph↗
arXiv2013

On the validity of the paraxial approximation for electron acceleration with radially polarized laser beams

In the study of laser-driven electron acceleration, it has become customary to work within the framework of paraxial wave optics. Using an exact solution to the Helmholtz equation as well as its paraxial counterpart, we perform numerical simulations of electron acceleration with a high-power TM01 beam. For beam waist sizes at which the paraxial approximation was previously recognized valid, we highlight significant differences in the angular divergence and energy distribution of the electron bunches produced by the exact and the paraxial solutions. Our results demonstrate that extra care has to be taken when working under the paraxial approximation in the context of electron acceleration with radially polarized laser beams.

physics.optics↗
arXiv2012

Electron acceleration driven by ultrashort and nonparaxial radially polarized laser pulses

Exact closed-form solutions to Maxwell's equations are used to investigate the acceleration of electrons in vacuum driven by ultrashort and nonparaxial radially polarized laser pulses. We show that the threshold power above which significant acceleration takes place is greatly reduced by using a tighter focus. Moreover, electrons accelerated by tightly focused single-cycle laser pulses may reach around 80% of the theoretical energy gain limit, about twice the value previously reported with few-cycle paraxial pulses. Our results demonstrate that the direct acceleration of electrons in vacuum is well within reach of the current laser technology.

physics.acc-ph↗
arXiv2004

Propagation of ultrashort electromagnetic wave packets in free space beyond the paraxial and slowly-varying-envelope approximations : a time-domain approach

A time-domain approach is proposed for the propagation of ultrashort electro- magnetic wave packets beyond the paraxial and the slowly-varying-envelope approximations. An analytical method based on perturbation theory is used to solve the wave equation in free space without resorting to Fourier trans- forms. An exact solution is obtained in terms of successive temporal and spatial derivatives of a monochromatic paraxial beam. The special case of a radially polarized transverse magnetic wave packet is discussed.

physics.optics↗