Coherent Optical Signatures of Electron Microbunching in Laser-Driven Plasma Accelerators
A. H. Lumpkin, M. LaBerge, D. W. Rule, R. Zgadzaj, A. Hannasch, O. Zarini, B. Bowers, A. Irman, J. P. Couperus Cabadağ, A. Debus, A. Köhler, U. Schramm, M. C. Downer
Abstract
We report observations of coherent optical transition radiation interferometry (COTRI) patterns generated by microbunched $\ensuremath{\sim}200\text{\ensuremath{-}}\mathrm{MeV}$ electrons as they emerge from a laser-driven plasma accelerator. The divergence of the microbunched portion of electrons, deduced by comparison to a COTRI model, is $\ensuremath{\sim}9\ifmmode\times\else\texttimes\fi{}$ smaller than the $\ensuremath{\sim}3\text{ }\text{ }\mathrm{mrad}$ ensemble beam divergence, while the radius of the microbunched beam, obtained from COTR images on the same shot, is $<3\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$. The combined results show that the microbunched distribution has estimated transverse normalized emittance $\ensuremath{\sim}0.4\text{ }\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$.