K.-C. Tzeng

The evolution of ultra‐intense, short‐pulse lasers in underdense plasmas

The propagation of short‐pulse lasers through underdense plasmas at ultra‐high intensities (I≥1019 W/cm) is examined. The pulse evolution is found to be significantly different than it is for moderate intensities. The pulse breakup is dominated by leading edge erosion and plasma wave wake formation rather than from Raman forward scattering type instabilities. A differential equation which describes local pump depletion is derived and used to analyze the formation and evolution of the erosion. Pulse erosion is demonstrated with one dimensional particle in cell (PIC) simulations. In addition, two dimensional simulations are presented which show pulse erosion along with other effects such as channeling and diffraction. Possible applications for plasma based accelerators and light sources are discussed.

Self-trapped electron acceleration from the nonlinear interplay between Raman forward scattering, self-focusing, and hosing

The generation of high current (>kA), relativistic beams from the wave breaking of plasma waves that result from a high-power (>5 TW), short-pulse (<ps) laser propagating through an underdense plasma is studied in detail using the fully explicit particle-in-cell model PEGASUS [K.-C. Tzeng et al., Phys. Rev. Lett. 76, 3332 (1996)]. The plasma waves and the self-trapped acceleration are due to a highly nonlinear interplay between Raman forward scattering, self-focusing, laser heating, hosing, and wave breaking. The resulting beams have a continuous energy spread with a maximum energy exceeding simple dephasing estimates. For a 5 J laser, a total of 2×1011 electrons are accelerated to relativistic energies with 2×108 of these at 50±1 MeV with a normalized emittance of 13π mm mrad. Details in the correlation of anti-Stokes generation and electron acceleration, the meaning of wave breaking, and the maximum electron energies are presented. A plasma wave accordion mechanism and multibunch beamloading can occur a...

Modeling single-frequency laser-plasma acceleration using particle-in-cell simulations: the physics of beam breakup

We investigate electron acceleration from space-charge waves driven by single-frequency lasers using a fully explicit particle-in-cell (PIC) model. The two dimensional (2-D) simulations model /spl sim/100 fs pulses at densities near n=4/spl times/10/sup 19/ cm/sup -3/ for 1-/spl mu/m lasers. The pulses are found to break up due to a combination of longitudinal and transverse bunching of the laser intensity via Raman forward scattering type instabilities. The ponderomotive force of these intensity modulations generates large amplitude plasma waves. Large numbers of self-trapped electrons and multiple Raman forward scattering satellites are observed. The relevance of these simulations to experiments is discussed.

Cathodeless, high brightness electron beam production by multiple laser beams in plasmas

The use of two crossed laser pulses in a plasma for the cathodeless production of high current low emittance electron beams is examined with fully relativistic 2-1/2D particle-in-cell (PIC) simulations. Estimates for the number of injected particles, their energy spread, and their emittance are given as functions of the amplitude and timing of the injection pulse relative to the drive pulse of the LWFA. The physical mechanism of the trapping of particles is examined based on single particle phase space trajectories in the self-consistent PIC simulations.

Theory and simulation of plasma accelerators

We report on some of the recent theoretical and computational results at UCLA and USC on plasma-based accelerator concepts. Topics discussed include beat-wave excitation from short-pulse lasers, self-trapped electron acceleration from self-modulational instabilities and wakefield excitation in preformed channels.