Requirements for a Stimulated Photon-Photon Scattering Experiment: Sensitivity Studies and Absolute Vacuum Generation

Stimulated photon-photon scattering (SPPS), a prediction of quantum electrodynamics that has never been directly measured, has been selected as a flagship experiment for the in-design, 2× 25-petawatt NSF OPAL laser. Virtual particles in the quantum vacuum may mediate the scattering of two real photons; SPPS includes a third "pump" beam to stimulate scattering in a known direction. Simulations of the preliminary SPPS design for NSF OPAL predict over 1000 scattered photons per shot. We present the results of sensitivity studies that establish co-pointing and co-timing requirements for the experimental facility. To limit background signal from residual gas molecules, a setup is proposed including two high-voltage capacitor plates and an additional ionizing laser pulse to temporarily clear the interaction region. We present simulations predicting that this approach can produce pure vacuum for more than 10 ns, as well as experiments to verify the vacuum-cleaning scheme in a laboratory setting.