Squeezed momentum distributions of relativistic electrons in intense laser fields with arbitrary polarization

Abstract

We investigate the dynamics of relativistic electrons interacting with intense laser fields in a linear or circular polarization. First, we study the momentum distributions of a single spatially localized wave packet. We find that these distributions are squeezed in the polarization plane ($y\text{\ensuremath{-}}z$) as well as along the laser propagation ($x$) direction. In a chosen gauge, the squeezing direction is controlled by the laser vector potential $\mathbf{A}$ and the electron initial momentum. For the case when the electron initial momentum is zero the squeezing occurs directly along the direction of $\mathbf{A}$. We obtain analytical expressions within linear momentum approximation that explain the squeezing features very well by defining a squeezing vector and rotational angle of the squeezed momentum distribution. We analyze the symmetric properties of the momentum distributions viewed in different momentum planes and discuss the effects of different helicity of circular laser polarizations and the direction of the spin quantization. An unexpected feature of bending of momentum distribution is found for very intense laser fields. We extend our investigation to the momentum distribution of two spatially separated wave packets, particularly the orientations of two crossing distributions. It is found that the absolute phase of the initial laser field affects the orientation of the electron momentum distributions while quantum superposition of two states with the same spin gives interference in the momentum distributions that depends on the quantum phase of the electron.