Ultra-low emittance beam generation using two-color ionization injection in a CO2 laser-driven plasma accelerator

TL;DR

This paper proposes a novel all-optical two-color ionization injection method in a plasma accelerator to generate ultra-low emittance electron beams, demonstrated with a CO2 laser and a frequency-doubled Ti:Al2O3 laser.

Contribution

It introduces a new two-color laser scheme for ionization injection that achieves ultra-low emittance beams in plasma accelerators.

Findings

Demonstrates the trapping and acceleration of electrons with low emittance.

Provides analytical expressions for beam emittance components.

Shows feasibility with a 10-micron CO2 laser and a frequency-doubled Ti:Al2O3 laser.

Abstract

Ultra-low emittance (tens of nm) beams can be generated in a plasma accelerator using ionization injection of electrons into a wakefield. An all-optical method of beam generation uses two laser pulses of different colors. A long-wavelength drive laser pulse (with a large ponderomotive force and small peak electric field) is used to excite a large wakefield without fully ionizing a gas, and a short-wavelength injection laser pulse (with a small ponderomotive force and large peak electric field), co-propagating and delayed with respect to the pump laser, to ionize a fraction of the remaining bound electrons at a trapped wake phase, generating an electron beam that is accelerated in the wake. The trapping condition, the ionized electron distribution, and the trapped bunch dynamics are discussed. Expressions for the beam transverse emittance, parallel and orthogonal to the ionization laser polarization, are presented. An example is shown using a 10-micron CO2 laser to drive the wake and a frequency-doubled Ti:Al2O3 laser for ionization injection.