Limits on low energy photon-photon scattering from an experiment on magnetic vacuum birefringence

Experimental bounds on induced vacuum magnetic birefringence can be used to improve present photon-photon scattering limits in the electronvolt energy range. Measurements with the Polarizzazione del Vuoto con Laser apparatus at both λ=1064 and 532 nm lead to bounds on the parameter Ae, describing nonlinear effects in QED, of Ae(1064)<6.6×10-21T-2@1064nm and Ae(532)<6.3×10-21T-2@532nm, respectively, at 95% confidence level, compared to the predicted value of Ae=1.32×10-24T-2. The total photon-photon scattering cross section may also be expressed in terms of Ae, setting bounds for unpolarized light of σγγ(1064)<4. 6×10-62m2 and σγγ(532)<2.7×10-60m2. Compared to the expected QED scattering cross section these results are a factor of 2×107 higher and represent an improvement of a factor about 500 on previous bounds based on ellipticity measurements and of a factor of about 1010 on bounds based on direct stimulated scattering measurements. © 2008 The American Physical Society.