Control over the polarization state of a femtosecond probe via pump-induced relativistic birefringence in underdense plasmas

Plasmas with an anisotropic relativistic momentum distribution exhibit polarization-dependent surface reflectivity and volumetric birefringence. Such momentum anisotropy can be induced via a pump laser pulse of relativistic intensity, thus enabling the temporal control over the polarization state of a simultaneous probe pulse in an underdense plasma. However, unlike in a spatially-uniform plasma, the probe pulse experiences an electron momentum distribution which may change rapidly in both time and space depending on their relative incidence angles. Thus, we investigate how these polarization-dependent optical properties for a femtosecond probe pulse depend on the pump intensity, ratio between the pump and probe wavelengths, incidence angles, and plasma density. We compare various analytic models for the transmitted probe's polarization state using one- and two-dimensional particle-in-cell simulations.