Monochromation of pulsed electron beams with terahertz radiation at a planar mirror

TL;DR

This paper introduces a novel method to significantly reduce electron beam energy spread using femtosecond photoemission and terahertz radiation interaction, enhancing electron spectroscopy and imaging precision.

Contribution

It presents an analytical and simulation-based approach to monochromate pulsed electron beams via terahertz interaction, achieving lower energy spread with minimal beam loss.

Findings

Energy spread reduced to tens of meV rms

Method requires only minor beam current loss

Analytical limits and non-ideal effects mapped

Abstract

Exquisite control of electron beam energy is required for many electron spectroscopy and imaging applications. For both continuous and pulsed beams, the beam energy spread is fundamentally limited by the electron source, and is typically a sizable fraction of an electron-volt. In this paper, we present a means to reduce electron beam energy spread after emission to the level of a few 10s of meV rms using femtosecond photoemission and an interaction with laser-derived single- to few-cycle terahertz (THz) radiation. We show analytically and in particle tracking simulations that this interaction can remove energy spread stored in both the transverse and longitudinal degrees of freedom. We analytically formulate the limit of energy spread that this technique can achieve, and map the non-ideal affects arising at high frequencies. The interaction is mediated by the beam's passage through a mirror which is reflective to terahertz radiation but allows transmission of the majority of the electron beam (e.g. a wire mesh). This method then only requires beam current losses of a few tens of percent, far smaller than what is achieved in prism and slit-based electron monochromators.