Observation of Laser-Pulse Shortening in Nonlinear Plasma Waves

Faure, Jérôme; Glinec, Yannick; Santos, J. J.; Ewald, Friederike; Rousseau, Jean‐Philippe; Kiselev, S. I.; Pukhov, A.; Hosokai, Tomonao; Malka, Victor

doi:10.1103/physrevlett.95.205003

Cited by 134 publications

(100 citation statements)

References 27 publications

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“…During the laser propagation, the laser pulse front begins to steepen due to the relativistic self-phase modulation and the high-density sheath at the front of the laser pulse (30), as shown in Fig. 3 I-L.…”

Section: Simulationsmentioning

confidence: 99%

Concurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble

Yan

Chen

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Desktop laser plasma acceleration has proven to be able to generate gigaelectronvolt-level quasi-monoenergetic electron beams. Moreover, such electron beams can oscillate transversely (wiggling motion) in the laser-produced plasma bubble/channel and emit collimated ultrashort X-ray flashes known as betatron radiation with photon energy ranging from kiloelectronvolts to megaelectronvolts. This implies that usually one cannot obtain bright betatron X-rays and high-quality electron beams with low emittance and small energy spread simultaneously in the same accelerating wave bucket. Here, we report the first (to our knowledge) experimental observation of two distinct electron bunches in a single laser shot, one featured with quasi-monoenergetic spectrum and another with continuous spectrum along with large emittance. The latter is able to generate high-flux betatron X-rays. Such is observed only when the laser self-guiding is extended over 4 mm at a fixed plasma density (4 × 10 18 cm −3 ). Numerical simulation reveals that two bunches of electrons are injected at different stages due to the bubble evolution. The first bunch is injected at the beginning to form a stable quasi-monoenergetic electron beam, whereas the second one is injected later due to the oscillation of the bubble size as a result of the change of the laser spot size during the propagation. Due to the inherent temporal synchronization, this unique electron-photon source can be ideal for pump-probe applications with femtosecond time resolution.S ynchrotron light sources are powerful in generating bright X-rays for a wide range of applications in basic science, medicine, and industry (1). However, these machines are usually large in size and expensive for construction and maintenance and are thus unaffordable to many would-be users. With the advent of tabletop ultrashort and ultraintense lasers, laser plasma acceleration (LPA) proposed by Tajima and Dawson (2) has demonstrated its great potential as a compact accelerator and X-ray source. Significant progress in LPA was made in the last decade (3-11): Well-collimated (approximately millirad) quasi-monoenergetic electron beams were first observed in 2004, and the electron energy above gigaelectronvolts over centimeter-scale acceleration lengths were demonstrated in several laboratories in the last few years.While accelerating longitudinally in the laser wakefield, the electron beams also oscillate transversally (wiggling motion) due to the transverse structure of the wakefield, which emits wellcollimated betatron X-rays (12-14). Among several mechanisms to generate X-ray radiation from laser-plasma interactions (15-20), betatron radiation is straightforward and able to deliver larger X-ray photon fluxes per shot [∼10 8 phs/shot (21)] and higher photon energies [up to gamma rays (22)]. The betatron oscillation frequency is given by ω β = ω p (2γ) −1/2 , where ω p is the plasma frequency and γ is the Lorentz factor of the accelerated electron beam. For large-amplitude betatron oscillations (i.e., a few mi...

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Section: Simulationsmentioning

confidence: 99%

Concurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble

Yan

Chen

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Even a Gaussian beam which is perfectly matched to the electron density gradient in which it propagates is not immune to nonlinear optical processes. Oscillations of the pulse spot-size due to non-linear refraction (Oguchi et al 2008;Zhidkov et al 2010;Kalmykov et al 2010), self-phase modulation leading to the formation of a relativistically intense optical piston (Tsung et al 2002;Lontano & Murusidze 2003;Faure et al 2005;Pai et al 2010;Vieira et al 2010;Kalmykov et al 2011a,b), and relativistic filamentation (Andreev et al 2007;Thomas et al 2007Thomas et al , 2009) are processes which result in pulse deformations. Electron self-injection appears to be extremely sensitive to such changes in pulse shape, which lead to contamination of the electron beam with polychromatic, poorly collimated background (Kalmykov et al 2011b).…”

Section: Benchmarkingmentioning

confidence: 99%

Computationally efficient methods for modelling laser wakefield acceleration in the blowout regime

Cowan¹,

Kalmykov

Beck

et al. 2012

J. Plasma Phys.

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Electron self-injection and acceleration until dephasing in the blowout regime is studied for a set of initial conditions typical of recent experiments with 100 terawatt-class lasers. Two different approaches to computationally efficient, fully explicit, three-dimensional particle-in-cell modelling are examined. First, the Cartesian code vorpal (Nieter & Cary 2004) using a perfect-dispersion electromagnetic solver precisely describes the laser pulse and bubble dynamics, taking advantage of coarser resolution in the propagation direction, with a proportionally larger time step. Using third-order splines for macroparticles helps suppress the sampling noise while keeping the usage of computational resources modest. The second way to reduce the simulation load is using reduced-geometry codes. In our case, the quasi-cylindrical code calder-circ (Lifschitz et al. 2009) uses decomposition of fields and currents into a set of poloidal modes, while the macroparticles move in the Cartesian 3D space. Cylindrically symmetry of the interaction allow using just two modes, reducing the computational load to roughly that of a planar Cartesian simulation while preserving the 3D nature of the interaction. This significant economy of resources allows using fine resolution in the direction of propagation and a small time step, making numerical dispersion vanishingly small, together with a large number of particles per cell, enabling good particle statistics. Quantitative agreement of the two simulations indicates that they are free of numerical artefacts. Both approaches thus retrieve physically correct evolution of the plasma bubble, recovering the intrinsic connection of electron self-injection to the nonlinear optical evolution of the driver.

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“…[31][32][33] Figures 5(a) and 5(b) show axial lineouts of normalized intensity and of the nonlinear index of refraction. The pulse leading edge witnesses the index downramp at all times.…”

Section: B Self-injection Into An Oscillating Bubble: Formation Of Qmentioning

confidence: 99%

“…Group velocity dispersion concurrently compresses the pulse. [31][32][33] Concomitant depletion of the leading edge further enhances pulse self-steepening. 6,34 The initially smooth driver turns into a relativistically intense "piston," which preaccelerates and compresses the initially quiescent electron fluid by its steep leading edge.…”

Section: Introductionmentioning

confidence: 99%

Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser-plasma acceleration in the blowout regime

et al. 2011

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Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser-plasma acceleration in the blowout regime" (2011 An electron density bubble driven in a rarefied uniform plasma by a slowly evolving laser pulse goes through periods of adiabatically slow expansions and contractions. Bubble expansion causes robust self-injection of initially quiescent plasma electrons, whereas stabilization and contraction terminate self-injection thus limiting injected charge; concomitant phase space rotation reduces the bunch energy spread. In regimes relevant to experiments with hundred terawatt-to petawatt-class lasers, bubble dynamics and, hence, the self-injection process are governed primarily by the driver evolution. Collective transverse fields of the trapped electron bunch reduce the accelerating gradient and slow down phase space rotation. Bubble expansion followed by stabilization and contraction suppresses the low-energy background and creates a collimated quasi-monoenergetic electron bunch long before dephasing. Nonlinear evolution of the laser pulse (spot size oscillations, self-compression, and front steepening) can also cause continuous self-injection, resulting in a large dark current, degrading the electron beam quality.

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Observation of Laser-Pulse Shortening in Nonlinear Plasma Waves

Cited by 134 publications

References 27 publications

Concurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble

Concurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble

Computationally efficient methods for modelling laser wakefield acceleration in the blowout regime

Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser-plasma acceleration in the blowout regime

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