Effect of pulse profile and chirp on a laser wakefield generation

Abstract

A laser wakefield driven by an asymmetric laser pulse with/without chirp is investigated analytically and through two-dimensional particle-in-cell simulations. For a laser pulse with an appropriate pulse length compared with the plasma wavelength, the wakefield amplitude can be enhanced by using an asymmetric un-chirped laser pulse with a fast rise time; however, the growth is small. On the other hand, the wakefield can be greatly enhanced for both positively chirped laser pulse having a fast rise time and negatively chirped laser pulse having a slow rise time. Simulations show that at the early laser-plasma interaction stage, due to the influence of the fast rise time the wakefield driven by the positively chirped laser pulse is more intense than that driven by the negatively chirped laser pulse, which is in good agreement with analytical results. At a later time, since the laser pulse with positive chirp exhibits opposite evolution to the one with negative chirp when propagating in plasma, the wakefield in the latter case grows more intensely. These effects should be useful in laser wakefield acceleration experiments operating at low plasma densities.

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

“…The higher amplitude wakefield serves to decrease the minimum momentum necessary to trap electrons. In addition, frequency chirping affects the laser group velocity, which could then influence the injection process [12,[32][33][34]. In our case, changing the pulse characteristics improved the energy and energy spread of the annulus but did not increase its charge.…”

“…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.…”

Simulation of a chirped femtosecond relativistic laser pulse interaction with underdense plasma by using a hydrodynamic approach

“…In addition, the stability of the electron beams was significantly improved in terms of energy, total charge, divergence, and beam pointing at an optimized spectral phase condition . Particle‐in‐cell (PIC) simulations have shown that a laser pulse with initial positive chirp generates a larger wakefield compared to negatively and un‐chirped pulses, thus leading to higher self‐trapped electrons, while the dark current in a LWFA can be suppressed by negatively chirped laser pulses . On the other hand, hydrodynamic approaches have been widely used to study the dynamics of the spatiotemporal evolution of an intense femtosecond laser pulse in an underdense plasma [see, e.g., refs .…”

Simulation study of wakefield generation by two color laser pulses propagating in homogeneous plasma

“…Therefore, enhancement of the generated wakefields by various techniques becomes important. [6][7][8] Significant research activities have been carried out in the last few decades in the areas of interaction of bi-color laser pulses with plasma. Rosenbluth and Liu 9 were the first to study the resonant excitation of plasma waves generated by beating of two long laser pulses having slightly different frequencies.…”