Effects of realistic laser intensity and phase distribution on high-charge laser wakefield acceleration

Laser wakefield acceleration (LWFA) can produce relativistic electron beams and various secondary particles in centimeter-long plasmas, making it a valuable particle source with important applications in many disciplines. In this work, we examine the effects of nonideal transverse intensity and phase distribution of laser pulses on LWFA through both experimental measurements and particle-in-cell simulations. The complex transverse profile of the 75 TW laser pulses reduces the self-focused intensity in the plasma compared with a transversely Gaussian laser pulse. Furthermore, the sheath structure of the nonlinear plasma wake excited by realistic laser pulses is wider and more complicated than that of a Gaussian laser pulse. These features hinder electron injection. As the laser pulse propagates through the plasma, its intensity profile gradually becomes elliptical and drives a plasma wake with a sharp sheath near the azimuths of the major axis, leading to electron injection. When using a realistic laser profile in simulations, both the charge and energy of injected electrons closely match experimental results ( ∼ 200 pC of charge and ∼ 200 MeV peak energy), whereas the Gaussian laser simulations produce much higher charge ( ∼ 500 pC ). Our findings reveal differences in injection dynamics between LWFA driven by nonideal laser pulses and those driven by Gaussian pulses and are useful for applications of LWFA that demand high-charge electron beams.