Observation of enhanced absorption of laser radiation by nano structured targets in PIC simulations

It is well known that Brunel’s vacuum heating mechanism is operative for laser energy absorption when the target plasma density rises sharply. For non-relativistic laser intensities and planar targets it is also necessary that the laser should strike the target at oblique incidence. The laser electric field at oblique incidence has a component normal to the surface to extract electrons from the target in the vacuum region for Brunel’s mechanism to be operative. At relativistic laser intensities, oblique incidence is not necessarily required as the J x B force is significant and can extract electrons from the target even when the laser is at normal incidence. In this manuscript, the interaction of short and intense laser pulse with structured overdense plasma targets have been studied using 2D particle-in-cell simulations. It is shown that for structured targets the absorption increases many fold. A detailed study and understanding of the absorption process for the structured targets in terms of structure scale length and amplitude have been provided.