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 [E. Zavattini et al., Phys. Rev. D 77, 032006 (2008)] 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^-21 T^-2@1064 nm and Aₑ⁽⁵³²⁾<6.3×10^-21 T^-2@532 nm, respectively, at 95% confidence level, compared to the predicted value of Aₑ=1.32×10^-24 T^-2. The total photon-photon scattering cross section may also be expressed in terms of Aₑ, setting bounds for unpolarized light of σ_γγ⁽¹⁰⁶⁴⁾<4.6×10^-62 m² and σ_γγ⁽⁵³²⁾<2.7×10^-60 m². 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.
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Bregant et al. (2008) studied this question.
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