Abstract
Relativistic laser interaction with micro- and nano-scale surface structures enhances energy transfer to solid targets and yields matter in extreme conditions. We report on the comparative study of laser-target interaction mechanisms with wire-structures of different size, revealing a transition from a coherent particle heating to a stochastic plasma heating regime which occurs when migrating from micro-scale to nano-scale wires. Experiments and kinetic simulations show that large gaps between the wires favour the generation of high-energy electrons via laser acceleration into the channels while gaps smaller than the amplitude of electron quivering in the laser field lead to less energetic electrons and multi-keV plasma generation, in agreement with previously published experiments. Plasma filling of nano-sized gaps due to picosecond pedestal typical of ultrashort pulses strongly affects the interaction with this class of targets reducing the laser penetration depth to approximately one hundred nanometers. The two heating regimes appear potentially suitable for laser-driven ion/electron acceleration schemes and warm dense matter investigation respectively.
Highlights
Relativistic interaction of an ultrashort laser pulse with micro- or nano-structured targets has recently stimulated a large interest for possible application in many fields, including Inertial Confinement Fusion[1], laser-driven ion/ electron acceleration[2, 3] or warm dense matter creation[4]
The formation of a preplasma before the arrival of the main laser peak can damage the structures on the target surface and fill the gaps between them, strongly affecting the interaction of the main peak
The (3/2)ω0 emission arises from the mixing of laser light with electron plasma waves produced by two-plasmon decay (TPD) instability[20]
Summary
Relativistic interaction of an ultrashort laser pulse with micro- or nano-structured targets has recently stimulated a large interest for possible application in many fields, including Inertial Confinement Fusion[1], laser-driven ion/ electron acceleration[2, 3] or warm dense matter creation[4]. The reason for such an interest lies in a more efficient absorption of the laser energy, if compared to a flat target. We show that wires gap and size significantly affect laser interaction with the electrons; while nano-wires/gaps, strongly affected by any residual pre-plasma, feature an efficient laser absorption via low-energy, few keV electrons and rapidly generate a hot dense plasma, micro-wires/gaps yield a cooler plasma and a high-energy electron component
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