Laser beam conditioning for two-color ionization injection in laser-plasma accelerators

We present recent experimental results from investigations of laser properties ideal for producing low emittance electron beams by two-color ionization injection in laser driven wakefield accelerators (LWFA). LWFA are next generation compact plasma based accelerators which have already begun contributing to a number of basic science, industry, security and medical applications. Many applications require high brightness beams enabled by low emittance. One proposal to achieve low emittance from an LWFA is a two-color laser configuration, where a long wavelength laser, with large ponderomotive force, is used to excite a plasma wakefield, while another trailing short wavelength laser is used to ionize inner shell electrons, injecting them in the accelerating phase of the wake [1]. The short wavelength allows for a high electric field for ionization, with low ponderomotive force. Results from experiments performed at BELLA Center include comparative measurements of wakefield generation by circularly and linearly polarized drive lasers, as well as measurements of generation of intense third harmonic pulses for controlled ionization.

[1] L.L. Yu, Two-Color Laser-Ionization Injection, PRL 112, 125001 (2014)