In this paper, through numerical simulation, the effect of initial phase on nonlinear Thomson scattering in a Gaussian laser pulse under tight focusing is studied. It is found for the first time that the initial phase is out of synchronization with the maximum radiation angle. When the initial phase changes from 360° to 180°, the maximum radiation distribution appears multi peak phenomenon, and the degree of the initial phase angle is different from that when the initial phase changes from 0 to 180 degrees., it shows an antisymmetric variation law. Furthermore, we discuss the process and reason of this phenomenon, which provides a accurate observation time and theoretical basis for high energy electron radiation experiment.
Nonlinear Thomson scattering in intense (𝑎0 = 6) single-cycle (𝐿0 = 1𝜇𝑚) Gaussian laser pulse is investigated theoretically and numerically that demonstrates varied spatial characteristics in the tightly focused (𝑏0 = 3𝜇𝑚) regime. In the above ultrashort laser pulse, the electron has the potential to radiate single attosecond pulse with almost infinite SNR which is highly robust to varied initial phases. Furthermore, a novel symmetry degradation phenomenon in the tightly focused domain is firstly discovered, where the fourfold symmetric spatial radiation pattern in non-tightly focused pulses respectively degrades to plane/linear symmetry radiation pattern in the spherical projected/polarized plane. While spatial radiation is highly sensitive to initial phases, we remarkably find that the difference of peak radiation’s polar angles 𝜙m exactly equals to that of incident laser’s initial phases 𝜙0, indicating the initial phase has phase/angle shift effect on the electron’s spatial motion and radiation. With numerical analysis, the sampling results demonstrate that peak radiation’s polar angle 𝜃m and the difference 𝜙m = 𝜙0 are constant regardless of initial phases.
The nonlinear Thomson backscattering process of electron under circularly polarized laser pulses is studied. The influence of the central collision position of the electron and laser pulses on the spectral characteristics of the scattered light is analyzed. The results show that the frequency broadening caused by doppler nonlinear frequency shift can be reduced and the monochromicity of the emitted light can be improved by adjusting the central collision position or the initial position of electron appropriately. At the same time, taking the requirements for the radiation intensity of scattered light into account, the optimal situation to generate quasi-monochromatic x-rays is presented. Besides, a scheme to increase the radiation energy of backscattered light by controlling the laser pulse width is proposed without changing the frequency band width. It provides a solution to overcome the problem that the radiation energy is too weak in the scheme of changing the initial position of electron. In addition, it was found that the interference fringes of the emitted light growing greatly as the pulse width increases.
Using the theory of single free electron in the form of Thomson scattering, through theoretical calculations and computer simulations, the properties of radiation pulses generated by ultrashort laser pulses are studied. Calculations show that in this case, the pulse width of the electron’s maximum radiation pulse reaches on the order of attosecond. We focus on nonlinear Thomson scattering. Under the condition of circularly polarized tightly focused laser pulses (b0 = 3λ0), we change the intensity of the incident laser. Generally, under the condition of relativistic laser intensity, keep the beam waist radius not changing, the larger the incident laser’s peak amplitude (a0), the larger the maximum of electron radiation power. After that, we focused on the temporal characters at the angle when the electron radiated power was at its maximum. At some special incident laser’s peak amplitude (a0), the change of pulse width in electron radiation power has some rules. We divide the change of pulse width into three categories according to the number of maximal values in the angular distribution of the radiation energy, and discuss the regularity of them separately.
Within the frame of electrodynamic and nonlinearly Thomson scattering, we study the initial phase-sensitivity with respect to spatial characteristics of a static electron irradiated by Guassian linearly polarized few-cycle laser pulse for different beam waists. With the combination and comparison of the electron's real-time motion and radiation conditions, the initial phase-sensitivity turns out with inverse proportional relation to the beam waist where the radiation’s transverse shift of varied initial phases is irregular in the non-tightly focused case. Furthermore, by changing the initial phases, the petal-like full spatial radiation pattern changes from 4 unstable pieces to 2 constant pieces and the radiated energy shift slows down with the beam waist evolving from b0 = 1 to b0 = 10. Finally, with initial phase 𝜙0 increasing from 0 to π we discover an interesting phenomenon for the first time, where the normalized maximal radiated power and corresponding azimuth angle fluctuate in the form of ripples and ladders in tightly-focused case b0 = 1, in contrast to the perfectly symmetry with respect to φ0 = 0.5π for the maximal radiated power in non-tightly focused case b0 = 10.
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