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Thomson scattering (TS) from electron beams produced in laser-plasma accelerators may generate femtosecond pulses of quasi-monochromatic, multi-MeV photons. Scaling laws suggest that reaching the necessary GeVelectron energy, with a percent-scale energy spread and five-dimensional brightness over 10^16 A/m^2, requires acceleration in centimeter-length, tenuous plasmas (n ~ 10^17 cm^-#3;3), with petawatt-class lasers. Ultrahigh per-pulse power mandates single-shot operation, frustrating applications dependent on dosage. To generate high-quality near-GeV beams at a manageable average power (thus affording kHz repetition rate), we propose acceleration in a cavity of electron density, driven with an incoherent stack of sub-Joule laser pulses through a millimeter-length, dense plasma …

Photon engineering can be exploited to control the nonlinear evolution of the drive pulse in a laser–plasma accelerator (LPA), offering new avenues to tailor electron beam phase space on a femtosecond time scale. One promising option is to drive an LPA with an incoherent stack of two sub-Joule, multi-TW pulses of different colors. Slow self-compression of the bi-color optical driver delays electron dephasing, boosting electron beam energy without accumulation of a massive low-energy tail. The modest energy of the stack affords kHz-scale repetition rate at manageable laser average power. Propagating the stack in a pre-formed plasma channel induces periodic self-focusing …