Hot-electron generation in copper and photopumping of cobalt

Hot electrons generated upon interaction of p-polarized 130 fs laser pulses with copper and penetrating into the target material are characterized wit h respect to their energy distribution and directionality. "Experimental" d ata are obtained by comparing the rear-side x-ray emission from layered tar gets with Monte Carlo electron-photon transport simulations. Theoretical el ectron energy distributions are derived by means of a one and a half-dimens ional particle-in-cell code. Both sets of data consist of a two-temperature distribution of electrons propagating in a direction almost perpendicular to the target surface. The "experimental" data contain a considerably highe r population of the lower temperature electrons. The discrepancy is explain ed by the intensity distribution of the laser spot. The results are used to design an experiment for demonstrating photopumping: of cobalt with copper K alpha radiation. A 10 mum copper foil is backed with 1 mm of polyethylen e (PE) followed by 10 mum of cobalt, the rear-side K alpha emission of whic h is measured. The PE layer prevents fast electrons from reaching the cobal t. Comparing the cobalt K alpha emission with that of nickel, which is not photopumped by copper K alpha shows enhancement by almost a factor of 2.