Non-linear photoemission from polycrystalline molybdenum irradiated by 790 nm–150 fs laser pulses

The total yield photoemission of a polycrystalline molybdenum sample irradiated by 790 nm–150 fs laser pulses is measured in the absence of space charge saturation. The extracted charge versus the laser intensity, measured over three decades of the extracted charge, which represents a significant extension of the previous experiments, gives us the opportunity to test the so-called thermally assisted non-linear photoemission model. The present results show non-linear photoemission behavior that can be explained, as expected, by a thermally assisted 3-photon emission. However a pure 4-photon emission could not be discarded. To take aim at clarifying this question the related non-linear coefficients are calculated and a scaling law for the probability of different multiphoton orders is proposed.