Floquet-Bloch theory of photoeffect in intense laser fields

A Floquet-Bloch analysis of intense-field photoemission of electrons from a model crystal surface is carried out. Simulations of electron emission spectra as a function of the laser intensity show several phenomena, including (a) the appearance of a sequence of emission bands, separated by bands of zero currents, at an interval of the photon energy, (b) a broad modulation of the envelope of the emission spectrum, and (c) the appearance of subbands within an emission band. The results are discussed and interpreted in terms of the field-modified band structure of the system. A comparison of the Floquet-Bloch model and the popular free-electron Sommerfeld model for intense-field photoeffect is made and the difference is shown to be of qualitative significance.