TEMPORAL EVOLUTION OF SELF-MODULATED LASER WAKEFIELDS MEASURED BY COHERENT THOMSON SCATTERING

Coherent Thomson scattering of a picosecond probe laser was used to me asure the time evolution of plasma wakefields produced by a high inten sity laser pulse (7 x 10(18) W/cm(2)) in an underdense plasma (m(e) ap proximate to 10(19) cm(-3)) in the self-modulated laser wakefield acce lerator configuration. Large amplitude plasma wakefields which lasted less than 5 ps were observed to decay into ion acoustic waves. The tim e scales associated with these measurements were consistent with the e ffects of the modulational instability and the enhancement of scattere d signal from plasma channel formation.