Experimental investigation on the origins of plasma-induced incoherence

Abstract

We present some results of a recent experiment performed on LULI's nanosecond laser chain which puts light on the underlying mechanisms involved in plasma-induced incoherence. Following theoretical interpretation for this new-found phenomenon, we set-up a Thomson scattering diagnostic off ion acoustic waves having small k-vectors transverse to the interaction beam. Such waves would be the product of the interplay between non-linear processes undergone by an RPP-smoothed laser beam propagating through an under-dense plasma. We have observed ion acoustic waves with k-vectors ranging from 0.4k0 to 0.6k0 located near the plasma's summit and occurring at the top of the interaction laser pulse. Good correlation between Thomson scattering spectra and other PII signatures, namely the redshift of the transmitted light, when varying interaction conditions strongly supports our first assumptions pertaining to the ion waves' participation in PII.