Energy spread of ultracold electron bunches extracted from a laser cooled gas

TL;DR

This paper measures the longitudinal energy spread of ultracold electron bunches from laser-cooled gases using a Wien filter, confirming theoretical predictions about factors influencing energy spread.

Contribution

First measurement of the energy spread of ultracold electron bunches using a specialized Wien filter, validating the theoretical model of energy spread dependence.

Findings

Measured relative energy spread of 0.64%

Wien filter calibration method developed

Results agree with theoretical model

Abstract

Ultrashort and ultracold electron bunches created by near-threshold femtosecond photoionization of a laser-cooled gas hold great promise for single-shot ultrafast diffraction experiments. In previous publications the transverse beam quality and the bunch length have been determined. Here the longitudinal energy spread of the generated bunches is measured for the first time, using a specially developed Wien filter. The Wien filter has been calibrated by determining the average deflection of the electron bunch as a function of magnetic field. The measured relative energy spread $\frac{\sigma_{U}}{U} = 0.64 \pm 0.09\%$ agrees well with the theoretical model which states that it is governed by the width of the ionization laser and the acceleration length.