Dichroism of the Vacuum

Abstract

Using Schwinger's expression for the Lagrangian density for the electromagnetic field in vacuum, including vacuum polarization effects, the imaginary part of the Lagrangian density is calculated to order $e^2$ from the pole contributions. It is found that in the presence of a strong electric field $E\sim \frac{\pi m^2}{e}\sim {10}^{16}$ V/cm, there is strong absorption of light polarized in a direction parallel to the electric field, the vacuum thus exhibiting a phenomenon analogous to dichroism in polaroids.