Figure 1
From: Stable femtosecond X-rays with tunable polarization from a laser-driven accelerator
Comparison of betatron oscillations in the transverse self-injection regime and the ionization-injection regime. (a, c) Schematic illustrations of the two injection mechanisms. In both cases, an intense femtosecond laser pulse, propagating in an underdense plasma, creates an ion cavity in its wake. For transverse self-injection a, electrons that get accelerated have to travel along the cavity sheath and enter the cavity at the back. Using Particle-in-cell simulations, it is found that these electrons originate from a ring-shaped region around the laser axis (b). In contrast, in the case of ionization-induced injection c, electrons are ionized inside the cavity, close to the maximum intensity of the laser. Injection can therefore occur longitudinally, and the initial position of trapped electrons is very different (d).
