The Thomson scattering spectra by an electron moving in the laser-magnetic resonance acceleration regime are computed numerically and analytically. The dependence of fundamental frequency on the laser intensity and magnetic resonance parameter is examined carefully. By calculating the emission of a single electron in a circularly polarized plane-wave laser field and constant external magnetic field, the scale invariance of the radiation spectra is evident in terms of harmonic orders. The scaling law of backscattered spectra are exhibited remarkably for the laser intensity as well for the initial axial momentum of the electron when the cyclotron frequency of the electron approaches the laser frequency. The results indicate that the magnetic resonance parameter plays an important role on the strength of emission. And the rich features of scattering spectra found may be applicable to the radiation source tunability.

By implementing the bremsstrahlung with Monte Carlo algorithm into the particle-in-cell code, the bremsstrahlung and nonlinear Compton scattering can be studied simultaneously in comparison way in the laser plasma interactions. The simulations are performed for the laser of different intensities interacting with either low-Z or high-Z target. The relative strength of the two photon emission from bremsstrahlung and nonlinear Compton scattering are compared. The result shows that when an ultrastrong intensity laser interacting with a thin and relative high Z target the nonlinear Compton scattering is dominant, however, when the laser intensity I < 10 22 W/cm 2 , the photon emission contributed by bremsstrahlung is comparable to that from nonlinear Compton scattering. In this case the usual ignorable of bremsstrahlung need to be reconsidered.

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The effects of super-cycle (or sub-cycle) and super-Gaussian laser pulse shapes on the forward Thomson scattering by an electron moving in a linearly polarized laser field are investigated. The numerical results show that for forward scattering spectra, there are only harmonics of odd orders. With increasing the super-cycle parameter, the intensity of the scattering spectra increases and more harmonics orders appear. In the case of sub-cycle laser pulse shape, decreasing the sub-cycle parameter leads to a gradual decrease in the interval between the adjacent harmonics and scattering spectra exhibiting quasi-continuity. Furthermore, the intensity of the high-order harmonic increases and the harmonic with peak intensity shifts from fundamental to higher order with increasing super-Gaussian parameter. Besides, the effects of the electron's initial direction and speed as well as the carrier envelope phase on the scattering spectra are also explored. Our results indicate the possibility of future application in X-ray source devices based on Thomson scattering.

A novel scheme assisted by an external axial magnetic field is proposed to accelerate and collimate protons when a right-hand circularly polarized laser irradiates on an overdense plasma. We find that the transition of heating electron mode plays an important role in proton acceleration. First, the electrons are accelerated by stochastic heating in the case of no external magnetic field. Second, when the ratio of electron cyclotron frequency in the external magnetic field to the laser frequency is smaller than the relativistic factor ωce/ω0≤γ, the cyclotron resonance absorption can occur and a laser front sharpening mechanism greatly improves the energy conversion from the laser to electrons. Meanwhile, the external magnetic field also restrains electrons' transverse motion. Finally, for ωce/ω0&gt;γ, there is a time delay in the electron heating, which can be divided into two stages. In the case of B = 2, a high quality proton beam can be harvested whose cut-off energy is enhanced by a factor of 4 and beam width is reduced to one fifth of that in the case of B = 0. These results may be helpful to understand the electron heating and proton accelerated process in a strongly magnetized plasma.