Bright 5 - 85 MeV Compton gamma-ray pulses from GeV laser-plasma accelerator and plasma mirror

Abstract

We convert a GeV laser-plasma electron accelerator into a compact femtosecond-pulsed ${\hat{I}}^3$-ray source by inserting a $100\hat{I}¼$m-thick glass plate $\sim 3$ cm after the accelerator exit. With near-unity reliability, and requiring only crude alignment, this glass plasma mirror retro-reflected spent drive laser pulses (photon energy $\hslash \ddot{I}{‰}_L=1.17$ eV) with $>50\%$ efficiency back onto trailing electrons (peak Lorentz factor $1000<{\hat{I}}_e^3<4400$), creating an optical undulator that generated $\sim 10^8{\hat{I}}^3$-ray photons with sub-mrad divergence, estimated peak brilliance $\sim 10^{21}$ photons/s/mm${}^2$/mrad${}^2$/$0.1\%$ bandwidth and negligible bremsstrahlung background. The ${\hat{I}}^3$-ray photon energy $E_γ= 4γ_e^2 \hbarω_L$, inferred from the measured ${\hat{I}}_e^3$ on each shot, peaked from 5 to 85 MeV, spanning a range otherwise available with comparable brilliance only from large-scale GeV-linac-based high-intensity ${\hat{I}}^3$-ray sources.