Modelling Subadditivity in Multiphoton Emission of Electrons from GaAs tips

Multiphoton emission of electrons are observed from sharp tips of heavily p-doped GaAs caused by laser pulses with, nominally, 800 nm wavelength, 1 nJ/pulse energy, and 90 fs duration. When the electron emission current due to two pulses separated by a delay 200 fs ≤ τ ≤ 1 ns is integrated over all electron energies, it is less than that observed for the sum of the emission from the two individual pulses. This subadditive behavior is consistent with a “fast” electron emission process, i.e. one in which the electron emission occurs over a time comparable to the laser-pulse width. In addition to this, a suppression of multiphoton emission was observed when an 800 nm wavelength continuous wave laser was coincident with a pulse laser. We have modeled these processes assuming either three- or four-photon emission, direct band-gap transitions, and electron and hole thermalization. The model predictions are in good qualitative agreement with our experimental data. We discuss possible use of the subadditivity effect caused by direct bandgap transitions to control photoemitted electron polarization [1].

[1] Brunkow et al. Appl. Phys. Lett., 114, 073502 (2019)