Single-photon and multiphoton processes causing resonance in the transmission of electrons by a single potential barrier in a radiation field

Abstract

Simulations of electrons tunneling in a barrier for which the height varies sinusoidally with time show resonances increasing the transmitted current. For square barriers, these resonances occur when electrons are promoted above the barrier by absorbing quanta from the barrier oscillations, and the barrier length is an integer multiple of one-half of the de Broglie wavelength. For several barriers having other profiles, we find that there is a single broad resonance centered at a wavelength equal to 0.9 times the wavelength for a photon having the energy to take the particle exactly to the top of the barrier. We attribute this difference to the fact that quanta may only be exchanged at the ends of a square barrier, whereas quanta are exchanged throughout the full length of barriers having other profiles—especially in regions of high electric field intensity. A Floquet expansion is used to examine the change in transmission caused by barrier modulation for electrons at the different energies caused by the exchange of quanta. We find that the wavelengths for resonance are proportional to the number of quanta absorbed by the particles, and attribute this observation to the requirement that specific values of absorbed energy are necessary for resonance. The increase in transmission caused by absorbing M quanta is proportional to the Mth power of the power flux density of the radiation causing barrier modulation. Thus, as the power is increased, the total transmission (including all energies) shows greater structure due to multiphoton processes. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 417–427, 1999