8 - Strong Field Interactions with Underdense Plasmas

Summary

In plasmas whose density is underdense the laser pulse can propagate through the plasma, depositing energy and driving plasma waves. The diverse effects seen in plasmas of this density regime are the subject of this chapter. The interplay of field ionization of a gas target, plasma heating and subsequent effects on laser propagation is scrutinized with phenomena such as plasma-induced defocusing and filamentation the subject of chapter sections. The self-consistent response of the plasma subject to a traversing intense pulse is modeled using the quasi-static approximation, illustrating how the ultrafast laser pulse can excite plasma waves. The impact of relativistic self-focusing is assessed and its interplay with those plasma waves discussed, leading to complex propagation effects. A section then addresses instabilities in the laser plasma interaction. The final sections of the chapter discuss how the production of these plasma wave wakefields can be used to accelerate electrons, with a range of regimes described ranging from linear, to nonlinear bubble and beatwave acceleration. A concluding section discusses betatron oscillations of electrons in the bubble acceleration regime.