In this paper we report a detailed description of the laser cleaning procedure
and emission performance measurement on a pulsed laser deposited Mg
film. During the tests performed after the end of each cleaning operation we
have observed an increase in quantum efficiency (QE) in time. Then the QE
apparently stabilizes at a remarkably higher value. The study of this
phenomenon and its relation to chemical composition of the residual gases
of vacuum environment is important because it determines both the
achievable QE value and the lifetime of the Mg film based cathode.
Moreover, the stability of the QE at remarkably high values has been
revealed for a time scale of several days after each laser cleaning process, in
our vacuum conditions. The adsorption of reactive chemical species leading
to the lowering of the Mg work function is discussed
