Abstract
Radiation losses in the interaction of superintense circularly polarized laser pulses with high-density plasmas can lead to the generation of strong quasistatic magnetic fields via absorption of the photon angular momentum (so-called inverse Faraday effect). To achieve the magnetic field strength of several Giga Gauss, laser intensities simeq 10^{24};mathrm {W/cm}^2 are required which brings the interaction to the border between the classical and the quantum regimes. We improve the classical modeling of the laser interaction with overcritical plasma in the “hole boring” regime by using a modified radiation friction force accounting for quantum recoil and spectral cut-off at high energies. The results of analytical calculations and three-dimensional particle-in-cell simulations show that, in foreseeable scenarios, the quantum effects may lead to a decrease in the conversion rate of laser radiation into high-energy photons by a factor 2–3. The magnetic field amplitude is suppressed accordingly, and the magnetic field energy—by more than one order in magnitude. This quantum suppression is shown to reach a maximum at a certain value of intensity and does not grow with the further increase in intensities. The non-monotonic behavior of the quantum suppression factor results from the joint effect of the longitudinal plasma acceleration and the radiation reaction force. The predicted features could serve as a suitable diagnostic for radiation friction theories.
Highlights
In a recent paper [30], we showed that radiation friction (RF) induces a specific form of the inverse Faraday effect (IFE), i.e., the generation of magnetic fields due to absorption of angular momentum into a plasma
By further developing the classical model for the calculation of radiation losses [31], we introduced a self-consistent picture of the IFE, accounting for RF effects on electron motion via the Zeldovich model [32], for the plasma motion driven by radiation pressure (“hole boring”) [33,34], and for the inhomogeneous distribution of the laser intensity
We include quantum effects in our theory and simulations using a semiclassical approach based on the modification of the RF force via the factor introduced by Ritus [35,36], as was done in the interpretation of experiments [18] and in other recent theoretical works [20,37]
Summary
In a regime of interaction with high-density plasmas, the conversion efficiency ηrad, see Eq (5) for the definition, of laser energy into incoherent radiation may be a few ten percent, which results in axial quasistatic magnetic fields up to gigagauss values at intensities 1024 W/cm, as observed in three-dimensional (3D) particle-in-cell (PIC) simulations with classical RF-included [30]. By further developing the classical model for the calculation of radiation losses [31], we introduced a self-consistent picture of the IFE, accounting for RF effects on electron motion via the Zeldovich model [32], for the plasma motion driven by radiation pressure (“hole boring”) [33,34], and for the inhomogeneous distribution of the laser intensity This improved model predicts values of ηrad in good agreement with the PIC simulations. We qualitatively probe possible manifestations of the quantum effects in the considered problem at intensities which leave the parameter χ < 1
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