Direct measurement of sub-10 fs relativistic electron beams with ultralow emittance

TL;DR

This paper demonstrates the generation and precise measurement of sub-10 femtosecond relativistic electron beams with ultralow emittance, advancing ultrafast electron beam technology.

Contribution

It introduces a method to produce and accurately measure sub-10 fs relativistic electron beams with ultralow emittance using a combination of laser-driven cathodes, velocity bunching, and high-voltage deflecting cavities.

Findings

Achieved ultralow normalized emittance ≤20 nm.

Produced electron bunches shorter than 10 fs rms.

Validated measurement technique with high-voltage deflecting cavity.

Abstract

Ultralow emittance ($\leq20$ nm, normalized) electron beams with $10^5$ electrons per bunch are obtained by tightly focusing an ultrafast ($\sim$ 100 fs) laser pulse on the cathode of a 1.6 cell radiofrequency photoinjector. Taking advantage of the small initial longitudinal emittance, a downstream velocity bunching cavity is used to compress the beam to $<10$ fs rms bunch length. The measurement is performed using a thick high voltage deflecting cavity which is shown to be well-suited to measure ultrashort durations of bunching beams, provided that the beam reaches a ballistic longitudinal focus at the cavity center.