Generation of Terawatt Attosecond Pulses from Relativistic Transition Radiation

When a femtosecond duration and hundreds of kiloampere peak current electron beam traverses the vacuum high-density plasma interface, new process, that we call relativistic transition radiation (RTR), generates an intense $\ensuremath{\sim}100$ as pulse containing $\ensuremath{\sim}1$ terawatt power coherent ultraviolet (VUV) accompanied by several smaller satellite pulses. This inherits radial polarization incident field has ring intensity distribution. RTR is emitted when density comparable to spot size much larger than skin depth. Physically, it arises from return or backward motion electrons starting just inside Doppler up shifts photons. The number pulses determined groups originate at different depths within first wake period emit coherently before phase mixing.