title: Collective polarization exchanges in collisions of photon clouds.
abstract: The one-loop "vacuum" Heisenberg-Euler coupling of four electromagnetic fields can lead to interesting collective effects in the collision of two photon clouds on a time scale order of magnitude faster than one estimates from the cross section and density. We estimate the characteristic time for macroscopic transformation of positive to negative helicity in clouds that are initially totally polarized and for depolarization of a polarized beam traversing an unpolarized cloud.
authors.affiliation: Department of Physics, University of California at Santa Barbara, Santa Barbara, California 93106, USA. sawyer@vulcan.physics.ucsb.edu
authors.forename: R F
authors.initials: RF
authors.lastname: Sawyer