Attenuation of ultraintense laser radiation in an assembly of molecular clusters

We present a theoretical and computational study of the effects of the laser light intensity attenuation, due to absorption by an assembly of (D2) n/2 (n=250- 3×104) clusters in ultraintense laser fields (peak intensity IM = 1016 - 1018 W cm-2). The laser intensity attenuation was described by a relation between the local, time-integrated energy flow of the laser pulse and the energy deposited per ion in the Coulomb explosion products. In the cluster vertical ionization (CVI) domain, the local laser intensity manifests a linear decrease along the plasma filament, so that under the conditions of partial light absorption the energy absorbed by the plasma filament is independent of the incident laser intensity. In the non-CVI domain, the local laser intensity decreases exponentially across the plasma filament and the energy absorbed is proportional to the incident intensity. Cluster sizes for total light absorption were established on the basis of numerical solutions of our first-order differential equation for the local laser intensity. The effect of strong light absorption on the kinetic energy distribution of the ions from Coulomb explosion in an assembly of clusters results in a marked deviation from the energy distribution under CVI conditions. This exhibits a sharp rise in the range of low energies with the location of a low-energy maximum in the energy distribution providing a benchmark for the assessment of the contributions of laser absorption effects. Finally, we consider the effects of laser light absorption in a single cluster, demonstrating that both in the CVI and in the non-CVI domains the attenuation of the laser intensity is small for the cluster sizes considered in this work, while in the non-CVI domain laser light absorption by a single large (R0 =330 0.3em and n∼ 5×106) deuterium cluster can be realized.