Photopumping of innershell transitions by relativistic plasmas

摘要

A 130 fs 200 mJ titanium saphire laser is used to investigate conditions of generating inversion on an innershell transition in cobalt Using a longitudinal pumping geometry copper K-shell radiation is used to photopump cobalt K_α. The amount of photopumping is determined by comparing the generated cobalt radiation with the one of nickel, for which photopumping by copper K_α is not possible. Using a specially designed target with a vacuum gap in between the pump and the medium to be pumped we observe a photopumped fraction of over 90%. The vacuum gap holds back the electrons which generate L-holes and thus destroy the inversion.