Formation Mechanism Analysis for Periodic Nano-Structure by Particle Simulations

Abstract

It was found in many experiments that repeated irradiations of short pulse lasers could form periodic nano-structures on metal surfaces and many formation mechanisms were suggested, but it is not fully understood yet. Therefore we use the two-dimensional PIC (Particle-In-Cell) code, in which equations of motion for charged particles and Maxwell equations for electromagnetic fields are simultaneously computed in two-dimensional space and three-dimensional velocity space, to simulate laser-plasma interactions and to investigate the formation mechanism of the nanostructure. When the laser intensity is relativistic, magnetic field and current density develop typical structures of the Weibel instability and it is found that this instability plays an important role to form the periodic nano-structure. On the other hand, it is also found that bi-directional surface plasma waves play a significant role together with the oscillating two-stream instability in the case of non-relativistic laser intensity.