Four-wave interaction in gas and vacuum: definition of a third-order nonlinear effective susceptibility in vacuum: chi((3))(vacuum)

Semiclassical methods are used to study the nonlinear interaction of light in vacuum in the context of four wave mixing. This study is motivated by a desire to investigate the possibility of using recently developed powerful ultrashort (femtosecond) laser pulses to demonstrate the existence of nonli near effects in vacuum, predicted by quantum electrodynamics (QED). An appr oach, similar to classical nonlinear optics in a medium, is developed in th is article. A third-order nonlinear effective susceptibility of vacuum is t hen introduced. (C) 1999 Published by Elsevier Science B.V. All rights rese rved.