Modulation of the current in a field emitter caused by a continuous wave or pulsed laser: Simulations and experimental results

Numerical simulations suggest that a laser would increase held emission current due to a resonant interaction in which tunneling electrons exchange quanta with the laser, and this has been confirmed experimentally. Floquet methods are used to determine the steady-state response to a cw laser, and the transient response to a laser pulse is computed with a product formulation that does not require absorbing boundary conditions or wave packets. Resonances in the steady-state response typically result in a single broad peak when the full distribution of energies in a metal are considered. The transient solutions show delays equal to the semiclassical tunneling time, which is defined as the time for traversing the inverted barrier. A 1 MHz tunneling current of 0.4 nA was measured when a tungsten field emitter with a dc current of 5 mu A was illuminated with a laser diode amplitude modulated at 1 MHz. The laser increases the de tunneling current by 270 nA, which is attributed to tip heating, but the rf current has a period much less than estimates of the thermal relaxation time. (C) 1997 American Vacuum Society.