Energy spectrum of photoelectrons produced by picosecond laser-induced surface multiphoton photoeffect

Photoelectrons were produced from a gold surface using strong picosecond Nd:glass laser pulses of ${10}^{10}$-W/${\mathrm{cm}}^2$ intensity. Unexpectedly high (up to 600 eV) energies were observed in the electron energy spectrum only when space-charge effects were completely eliminated. This result is compared with the well-known electron energy spectra of the multiphoton ionization of gases.