Threshold of induced transparency in the relativistic interaction of an electromagnetic wave with overdense plasmas

Abstract

An exact analytical investigation of the stationary solutions describing the interaction between high-intensity laser radiation and an overdense plasma is presented. Both the relativistic and striction nonlinearities are taken into account, and their joint action gives rise to a solitary solution. This solution clearly shows that there exists an inherent limit of the induced transparency on the density of the overdense plasma in order to obtain a stationary physical solution. Furthermore, it is found that the striction nonlinearity tends to create a strong peaking of the plasma electron density, which suppresses the laser penetration and significantly enhances the threshold intensity for induced transparency.

Production of high energy protons with hole-boring radiation pressure acceleration

“…The threshold for HB RPA is in very good agreement with Cattani's prediction for the penetration threshold of such pulses. 18 We have also shown that longer laser wavelengths might be exploited to reach higher energies. At a laser wavelength of 1 lm and I % 1 Â 10 21 W cm À2 one can produce proton bunches with average proton energies up to about 70 MeV via HB RPA, at 2 lm this becomes 125 MeV.…”

“…In the case of a thick target, as we are concerned with here, it was predicted, by Cattani et al, 18 that penetration of a laser pulse will be prevented by compression of electrons at a density somewhat lower than the relativistically corrected critical density. The expression given in Ref.…”

“…We have studied this threshold by carrying out further simulations over the intensity range of a 0 ¼ 30-60 (I ¼ 1-5 Â 10 21 W cm À2 . It was found that Cattani's expression 18 (plotted in Fig. 1) provides a very good indication of where this threshold lies.…”

“…Although one may think that such a plasma will be relativistically transparent, it has been shown theoretically that even very intense pulses cannot penetrate a plasma somewhat below the relativistically corrected critical density. 18 We exploit this result to achieve high proton energies via density reduction.…”

Ion acceleration in electrostatic field of charged cavity created by ultra-short laser pulses of 1020–1021 W/cm2

“…In such concept the effect of plasma Coulomb field in self-induced transparency is ignored, which instead became recently a topic of intense research [19][20][21][22][23]. The ponderomotive force pushes the electrons deep into the target in the form of a moving electron density spike and produces a charge separation layer (a cavity in a realistic 3D geometry) extending from the target's edge to the laser pulse front.…”