Quantum Electrodynamics (QED) predicts that the vacuum should behave as a nonlinear optical medium: the speed of light in a vacuum should decrease when the vacuum is subjected to intense electromagnetic fields. This remarkable property of the vacuum has yet to be observed.
The DeLLight (Deflection of Light by Light) experiment aims to measure this effect using ultra-intense femtosecond laser pulses delivered by the LASERIX platform at the IJCLab laboratory (Université Paris-Saclay). DeLLight's innovative method involves measuring, by interferometry, the refraction of a low-energy (probe) laser pulse, induced by the refractive index gradient of the vacuum produced by a high-intensity external (pump) pulse. The refraction of the probe pulse is detected using a Sagnac interferometer.
In this seminar, I will begin by discussing the scientific motivations behind studying the optical index of the vacuum and the few existing experimental tests. I will then describe the experimental method and the technical challenges of the DeLLight project. Finally, I will present recent results from DeLLight measurements in a low-energy gas, obtained from the pilot experiment, which validate the experimental method.