Stable, tunable, quasimonoenergetic electron beams produced in a laser wakefield near the threshold for self-injection

Abstract

Stable operation of a laser-plasma accelerator near the threshold for electron self-injection in the blowout regime has been demonstrated with 25-60 TW, 30 fs laser pulses focused into a 3-4 millimeter length gas jet. Nearly Gaussian shape and high nanosecond contrast of the focused pulse appear to be critically important for controllable, tunable generation of 250-430 MeV electron bunches with a lowenergy spread, $10 pC charge, a few-mrad divergence and pointing stability, and a vanishingly small low-energy background. The physical nature of the near-threshold behavior is examined using threedimensional particle-in-cell simulations. Simulations indicate that properly locating the nonlinear focus of the laser pulse within the plasma suppresses continuous injection, thus reducing the low-energy tail of the electron beam.

Compact source of narrowband and tunable X-rays for radiography

“…The beam has an angular spread of <5 mrad and maximum photon energy extending to 14 MeV with a quasimonoenergetic feature at 13 MeV. The total photon number for this shot is estimated to be 10 6 . Under optimal conditions, we have measured >10 7 photons per laser shot.…”

“…The all-optical architecture comprises two high-intensity laser pulses. One laser pulse is focused to relativistic intensity (electrons oscillate in the laser field with a velocity close to the speed of light) and interacts with a supersonic gas jet to generate quasi-monoenergetic electron beams by the process of laser wakefield acceleration [5,6]. The second laser pulse, also focused to high-intensity, scatters off the laser-driven electron beam.…”

Optical control of electron phase space in plasma accelerators with incoherently stacked laser pulsesa)

“…Specific examples of this tunability, associated with the pulse transient dynamics in a finite-length plasma, have been recently observed in experiments. [29][30][31][32] Using plasmas as nonlinear optical devices [33][34][35][36][37] and tailoring relativistic optical processes responsible for the pulse evolution [24][25][26][27] presents an opportunity to realize compact, flexible, high-repetition rate sources of high-quality, high-energy electron beams while reducing the need for high-average power lasers. 38 The ongoing quest for ever higher electron energies 39,40 (a fundamental requirement of advanced radiation sources 3,4,[41][42][43][44][45] dictates the use of petawatt-power lasers and centimeter-scale plasmas.…”

High-Flux Femtosecond X-Ray Emission from Controlled Generation of Annular Electron Beams in a Laser Wakefield Accelerator

“…In this regime, plasma waves propagate at near-luminous speed and evolve synchronously with the optical driver, readily trapping initially quiescent background electrons [10]. The self-injection process (which defines the beam phase space structure) can thus be controlled by modifying the drive pulse parameters, such as chirping the frequency [11], shaping the pulse temporal profile [12], and changing the focusing geometry [13][14][15]. This process can also be accomplished by tailoring the plasma density profile.…”