Two-color ionization injection in a multi-pulse-driven laser-plasma accelerator*

Laser plasma accelerators (LPAs) have promise to be the next generation accelerator for a number of basic science, industry, security and medical applications. Not only are these accelerators extremely compact, they offer a path to orders of magnitude increase in brightness compared to conventional accelerators, enabled by low emittance and high peak current.  High peak current naturally comes from the femtosecond length of LPA electron beams, but beam emittance needs to be improved. One proposal to achieve ultra-low emittance from a laser plasma accelerator is an all optical, two laser configuration, where one is used to generate a plasma wake, while another, with low ponderomotive potential but high electric field, locally ionizes inner shell electrons, injecting them in the accelerating phase of the wake [1].  Since the electric field is proportional to the ponderomotive potential and inversely proportional to the wavelength, a high electric field with low ponderomotive potential can be achieved by using a smaller wavelength.  We will present plans at BELLA Center to demonstrate this technique using pulses  from a Ti:Sapphire laser system to generate the wake, and a third harmonic pulse to locally inject electrons into the wake.  

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