Generation of terawatt, attosecond pulses from relativistic transition radiation

TL;DR

This paper introduces relativistic transition radiation (R-TR), a novel process generating terawatt, attosecond pulses of coherent VUV radiation with ring-shaped intensity distribution when an ultrashort, high-current electron beam interacts with a plasma interface.

Contribution

It presents the discovery and analysis of R-TR, a new radiation mechanism producing intense, ultrashort pulses with unique polarization and spatial characteristics in plasma-electron beam interactions.

Findings

Generation of ~100 as pulses with TW power

Ring-shaped intensity distribution of emitted radiation

Dependence of pulse number on plasma electron groups

Abstract

When a fs duration and hundreds of kA peak current electron beam traverses the vacuum and high-density plasma interface a new process, that we call relativistic transition radiation (R-TR) generates an intense $\sim100$ as pulse containing $\sim$ TW power of coherent VUV radiation accompanied by several smaller fs duration satellite pulses. This pulse inherits the radial polarization of the incident beam field and has a ring intensity distribution. This R-TR is emitted when the beam density is comparable to the plasma density and the spot size much larger than the plasma skin depth. Physically, it arises from the return current or backward relativistic motion of electrons starting just inside the plasma that Doppler up-shifts the emitted photons. The number of R-TR pulses is determined by the number of groups of plasma electrons that originate at different depths within the first plasma wake period and emit coherently before phase mixing.