Measurement of deflection on germanium and gold prisms using 1.7 MeV laser Compton scattering γ-rays

We measured the refractive index of germanium and gold prisms at 1.7 MeV to explore if there are refractive index enhancements to 6th power of atomic number due to high order nonlinear process of Delbrück scattering in quantum electrodynamics. We measured the deflection by prisms using imaging plates and laser Compton scattering γ-rays with linear and random polarization. We used crystal and polycrystalline prisms for Au. The measured upper limit of the refractive index, δ, for crystal Ge, crystal Au, or polycrystal Au prisms is 4.0×10−8, 2.9×10−7, or 2.4×10−7. We could not find any signature for high order nonlinear process. This result does not support the hypothesis suggested by Habs et al. (2012) [3].