Low emittance electron beam generation from a laser wakefield accelerator using two laser pulses with different wavelengths

Abstract

Ionization injection triggered by short wavelength laser pulses inside a nonlinear wakefield driven by a longer wavelength laser is examined via multidimensional particle-in-cell simulations. We find that very bright electron beams can be generated through this two-color scheme in either collinear propagating or transverse colliding geometry. For a fixed laser intensity I, lasers with longer/shorter wavelength λ have larger/smaller ponderomotive potential (∝ Iλ 2 ). The two-color scheme utilizes this property to separate the injection process from the wakefield excitation process. Very strong wakes can be generated at relatively low laser intensities by using a longer wavelength laser driver (e.g., a 10 μm CO 2 laser) due to its very large ponderomotive potential. On the other hand, a short wavelength laser can produce electrons with very small residual momenta (p ⊥ ∼ a 0 ∼ ffiffi I p λ) inside the wake, leading to electron beams with very small normalized emittances (tens of nm). Using particle-in-cell simulations we show that a ∼10 fs electron beam with ∼4 pC of charge and a normalized emittance of ∼50 nm can be generated by combining a 10 μm driving laser with a 400 nm injection laser, which is an improvement of more than 1 order of magnitude compared to the typical results obtained when a single wavelength laser is used for both the wake formation and ionization injection. With the transverse colliding geometry, simulations show that similarly low emittance and much lower slice energy spread (∼30 keV, comparing with the typical value of few MeV in the longitudinal injection scheme) can be simultaneously obtained for electron beams with a few pC charge. Such low slice energy spread may have significant advantages in applications relevant to future coherent light sources driven by plasma accelerators.

Mid-infrared lasers for energy frontier plasma accelerators

“…Oversized plasma bubbles to be readily produced by CO 2 lasers will sustain high-current electron bunches. The same feature, combined with localized injecting of seed electrons by means of external laser ionization in two-color LWFA scheme [48,49], might support acceleration of low-emittance electron bunches. This capability of a low-density LWFA combined with the proportional to λ copious number of photons per energy unit from another counter-propagating CO 2 laser pulse, promises the highest gamma-or x-ray yield in inverse Compton scattering considered for compact light sources.…”

Laser wakefield and direct acceleration with ionization injection

“…is the transverse laser profile normalized as g(z = 0) = 1, we obtain [40,41] ( ) . Therefore, those electrons born far off-axis are likely to be produced by peak-phase ioniz ation and to have small p z0 .…”

Electron Injection for Direct Acceleration by A Gaussian Laser Field Under the Influence of Azimuth Magnetic Field

“…An electron while interacting with CP laser pulse experiences a force due to longitudinal component of electric field of laser. Ionization injection induced by short wavelength laser pulses inside a nonlinear wakefield driven by a longer wavelength laser was investigated using multidimensional particle-in-cell (PIC) simulations and generation of very bright electron beams in either collinear propagating or transverse colliding geometry revealed [16]. Ultra-intense radially polarized (RP) laser beam has a strong longitudinal field component at the axis of the beam for accelerating electrons and among the various laser acceleration configurations it is very promising [17][18][19].…”