Phase dependence of relativistic electron dynamics and emission spectra in the superposition of an ultraintense laser field and a strong uniform magnetic field.

The phase dependence of the dynamics and emission spectra of a fully relativistic electron in the superposition of an ultraintense plane wave laser field and a strong uniform magnetic field has been investigated. It is found that the effect of changing the initial laser phase is quite different for circularly and linearly polarized laser fields. For circular polarization only the axis of the helical trajectory is changed with variation of the initial laser field phase. However, for linear polarization, the effect of changing the initial phase is opposite in the two parameter regions divided by the resonance condition r=1 (r stands for the ratio between the reduced cyclotron frequency and laser frequency). When r<1, with increase in the initial laser field phase eta(0) from 0 to pi/2, both the radius of the electron's helical trajectory and the height of the peak related to the uniform magnetic field are decreased, and these two physical values are increased with an increase in the laser initial phase when r>1. The phase dependence of the electron's energy and velocity components was also studied. Some beat structure is found when eta(0)=0 and this structure is absent when eta(0)=pi/2.