Nonlinear photoemission from polycristalline molibdenum 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. (C) 2001 Elsevier Science Ltd. All rights reserved.