Summary form only given. We report the results of a study of semitransparent films of nickel of varying thickness using femtosecond time-resolved polarimetry. For the first time we have combined transmission and reflection measurements, and have studied glass and air interfaces of nickel films of different thicknesses. We have identified importance of the surface contribution to the film nonlinearity, and have also observed that not only the magnitude of the cubic nonlinearity in nickel, but even its sign could be different depending on the nature of the interface. We also saw that both bulk and surface components of the cubic optical nonlinearity in nickel films are exceptionally fast with relaxation times shorter than /spl sim/40 fs.
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