Photopumping of innershell transitions by relativistic plasmas

A 130 fs 200 mJ titanium saphire laser is used to investigate conditions of generating inversion on an innershell transition in cobalt. Using a longit udinal pumping geometry copper K-shell radiation is used to photopump cobal t K-alpha. The amount of photopumping is determined by comparing the genera ted cobalt radiation with the one of nickel, for which photopumping by copp er K-alpha 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 photopump ed fraction of over 90 %. The vacuum gap holds back the electrons which gen erate L-holes and thus destroy the inversion.