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

The total yield photoemission of a polycrystalline molybdenum sample irradi ated by 790 nm-150 fs laser pulses is measured in the absence of space char ge saturation. The extracted charge versus the laser intensity, measured ov er three decades of the extracted charge, which represents a significant ex tension of the previous experiments, gives us the opportunity to test the s o-called thermally assisted non-linear photoemission model. The present res ults show non-linear photoemission behavior that can be explained, as expec ted, by a thermally assisted 3-photon emission. However a pure 4-photon emi ssion could not be discarded. To take aim at clarifying this question the r elated non-linear coefficients are calculated and a scaling law for the pro bability of different multiphoton orders is proposed. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.