369 / 2019-02-28 10:31:37

On the mechanism of energetic electron and X-ray beam production by intense laser irradiation of nanostructured targets

relativistic laser radiation,nanostructured target,laser-target interaction,PIC simulation

全体主题 > Fundamental Physics at Extremes

Experiments and numerical simulations demonstrate that the irradiation of nanostructured targets with the relativistic-intensity laser pulses can provide large conversion ratio of the laser energy into the energy of highly energetic electron and X-ray beams (e.g. see Ref. 1, 2 and the references therein).
Although, the PIC simulations seem to confirm the experimental results of high laser radiation absorption by nanostructured targets and provide some details of the laser-target interactions the main mechanisms of electron acceleration and high laser energy conversion to energetic electron and X-ray beams are still poorly understood.
To elucidate the physical mechanisms of intense laser interactions with nanostructured targets we perform the set of 2D PIC simulations with two different morphology of nanostructured targets: straight tendrils and wavy tendrils, which resemble the structures of “fuzz” observed in the course of tungsten irradiation with helium plasma (e.g. see Ref. 3 and the references therein). We considered both s- and p- polarized (with respect to 2D tendril structure) laser radiation of 5e19 W/cm2 . In addition, we varied the characteristic radius of the tendrils, d , and the inter- tendrils distance, D, within the range 10-80 nm and 25-800 nm respectively. We found that for a given laser wavelength (400 nm), both absorption of laser radiation and it's conversion efficiency to energetic electron and X-ray beams have strong dependence on both d , and D values.
We perform careful analysis of the physical picture of laser-nanostructures target interactions emerging from our simulations and make both the detail comparison of the results of our PIC simulations with some theoretical models (e.g. see Ref. 1, 2 and the references therein) of the mechanisms responsible for the laser radiation absorption and the generation of energetic electron and X-ray beams via laser interaction with nanostructured targets and present the results of our analysis.

Acknowledgments
A.K. is thankful to Dr. Daiki Kawahito and Prof. Alexey Arefiev and the members of his group for the discussions on the PIC simulations. This work was supported by the University of California Office of the President Lab Fee Grant No. LFR-17-449059.

Keywords: relativistic laser radiation, nanostructured target, laser-target interaction, PIC simulation

[1] G. Cristoforetti et al, “Transition from Coherent to Stochastic electron heating in ultrashort relativistic laser interaction with structured targets”, Scientific Reports 7, (2016) 1479, DOI:10.1038/s41598-017-01677-5
[2] A. A. Andreev and K. Yu. Platonov, “Interaction of a High-Intensity Ultrashort Laser Pulse with Extended Nanofilaments of Dense Plasma”, Nonlinear and Quantum Optics, 117, (2014) 287.
[3] M. J. Baldwin and R. P. Doerner, “Helium induced nanoscopic morphology on tungsten under fusion relevant plasma conditions” Nucl. Fusion 48 (2008) 035001.