We study the perspectives of measuring the phenomenon of vacuum birefringence predicted by quantum electrodynamics using an x-ray free-electron laser (XFEL) alone. We devise an experimental scheme allowing two consecutive XFEL pulses to collide under a finite angle. and thus act as both pump and probe field for the effect. The signature of vacuum birefringence is encoded in polarizati... https://www.foldlyers.shop/product-category/iphone-7-8/