Nonlinear laser-driven wakefields with arbitrary phase velocity

The flying focus technique can generate laser pulses where the group velocity can take any value – even superluminal – independently from its phase velocity. These pulses are generating significant interest as they can be used to enhance the acceleration in laser-plasma accelerators (e.g. by enabling dephasingless acceleration in laser wakefields [J. Palastro et al, PRL 2021]) or to enhance the acceleration quality by avoiding dark currents (e.g. by using a superluminal driver [J. Palastro et al, PoP 2021]). Because these pulses promise to open new regimes in other areas, new techniques were developed and experimentally tested to generate laser pulses with arbitrary group velocities [e.g. H. Kondacki et al, Nature Comms 2019].

To investigate in detail how these pulses involve in the plasma at any intensity, it is important to incorporate these pulses into particle-in-cell (PIC) codes. Here, we implement a laser pulse that can travel at arbitrary velocities in OSIRIS. The implementation relies on a suitable superposition of plane waves oriented along with different angles. It works in 2D and 3D geometries. Using this feature, we show that these lasers can excite wakefields with controllable phase velocities, and investigate their properties as a function of the wake phase velocity.