Pair creation and an x-ray free electron laser - art. no. 193902

Using a quantum kinetic equation we study the possibility that focused beam s at proposed x-ray free electron laser facilities can initiate spontaneous electron-positron pair production from the QED vacuum. Under conditions re ckoned achievable at planned facilities, repeated cycles of particle creati on and annihilation will take place in tune with the laser frequency. The p eak particle number density is insensitive to this frequency, and one can a nticipate the production of a few hundred particle pairs per laser period.