High current density produced by femtosecond nonlinear single-photon photoelectric emission from gold

The sensitivity of single-photon photoelectric emission of pure-polycrystalline Au induced by a KrF excimer laser emitting at 248 nm pulses of 450 fs duration, has been measured. A nonlinear increase of photoelectric efficiency as a function of the laser peak intensity has been observed. The threshold of this nonlinearity is estimated from the experimental data to be slightly less than 0.1 GW/cm2. This value is in good agreement with earlier observations for W and Zr. We demonstrate that this is the direct consequence of nonequilibrium electron and lattice temperatures produced at the surface by the subpicosecond laser pulses.