Our simulations of laser-assisted tunneling show a resonance in which the tunneling current is significantly increased. This resonance is caused by reinforcement of the wavefunction, and the criterion for square barriers is that the barrier length is an integral multiple of one-half the de Broglie wavelength for tunnelling particles that are promoted above the barrier by absorbing single quanta from the radiation field. Simulations of laser-assisted field emission suggest that a laser pulse can switch tunneling currents in less than 10 fs, and that photomixing could be used to generate and detect ultrawide-band signals from DC to 100 THz. Delays of several fs associated with these effects have fundamental significance regarding the tunneling process. We have demonstrated the resonance experimentally by modulating the tunneling current from a sharp tungsten field emitter tip with a laser, and the data are in reasonable agreement with the simulations. We have also examined the resonance experimentally in laser-assisted scanning tunneling microscopy where our simulations suggest that the mixing signal may be increased by 70-90 dB when compared with presently used techniques.