Abstract
The relativistic Doppler effect is one of the most famous implications of the principles of special relativity and is intrinsic to moving radiation sources, relativistic optics and many astrophysical phenomena. It occurs in the case of a plasma sail accelerated to relativistic velocities by an external driver, such as an ultra-intense laser pulse. Here we show that the relativistic Doppler effect on the high energy synchrotron photon emission (~10 MeV), strongly depends on two intrinsic properties of the plasma (charge state and ion mass) and the transverse extent of the driver. When the moving plasma becomes relativistically transparent to the driver, we show that the γ-ray emission is Doppler-boosted and the angular emission decreases; optimal for the highest charge-to-mass ratio ion species (i.e. a hydrogen plasma). This provides new fundamental insight into the generation of γ-rays in extreme conditions and informs related experiments using multi-petawatt laser facilities.
Highlights
The relativistic Doppler effect is one of the most famous implications of the principles of special relativity and is intrinsic to moving radiation sources, relativistic optics and many astrophysical phenomena
It has been shown that under these given conditions, the radiation reaction (RR) force can counteract the ponderomotive force and leads to the formation of a confined electron bunch propagating behind the laser pulse front[26]
In the case of a thin plasma layer accelerated by a driving force, we have reported on the influence of the ion charge-to-mass ratio and the transverse extent of the driver on the relativistic Doppler-boosted synchrotron radiation
Summary
The relativistic Doppler effect is one of the most famous implications of the principles of special relativity and is intrinsic to moving radiation sources, relativistic optics and many astrophysical phenomena. Such ultra-intense laser radiation will enable the laboratory production of extreme conditions in which collective effects are paramount, accessing physics similar to that encountered in astrophysical events[8,9,10]. × B is defined as the electric field in the electron’s ~ 1016 Vcm−1 11, where γe is the electron Lorentz factor and E⊥ is the electric field perpendicular to the electron’s motion This results in the production of copious amounts of synchrotron-like γ-ray emission[12,13,14,15,16] and electron-positron pairs as χe tends to unity[17,18,19,20]. The radiation reaction, which can be interpreted as a friction force in the semi-classical framework (recently shown to accurately describe the average energy loss of the electron population22,23), which strongly affects the electron dynamics[24,25,26,27] and those of ions, through the charge-displacement-induced fields[28,29,30]
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