# Knife-edge based measurement of the 4D transverse phase space of electron beams with picometer-scale emittance

## TL;DR

This paper introduces a novel measurement technique for 4D transverse phase space of electron beams with picometer-scale emittance, enabling detailed characterization of ultrabright, ultrafast electron pulses for advanced scientific applications.

## Contribution

A new method for reconstructing the 4D transverse beam matrix of strongly correlated electron beams with sub-nanometer emittance.

## Key findings

- Successfully reconstructed 4D transverse phase space with sub-nanometer emittance.
- Demonstrated capability to characterize beams with sub-micrometer spot size.
- Extended ultrafast electron diagnostics into picometer-range emittance.

## Abstract

Precise manipulation of high brightness electron beams requires detailed knowledge of the particle phase space shape and evolution. As ultrafast electron pulses become brighter, new operational regimes become accessible with emittance values in the picometer range, with enormous impact on potential scientific applications. Here we present a new characterization method for such beams and demonstrate experimentally its ability to reconstruct the 4D transverse beam matrix of strongly correlated electron beams with sub-nanometer emittance and sub-micrometer spot size, produced with the HiRES beamline at LBNL. Our work extends the reach of ultrafast electron accelerator diagnostics into picometer-range emittance values, opening the way to complex nanometer-scale electron beam manipulation techniques.