Measurements of modulation of the total emitted current in laser-assisted field emission

A laser diode (690 nm, 14.4 mW) was focused on a tungsten field emitting tip in vacuum, and the time-dependent emitted current was measured when the laser diode was amplitude modulated at a frequency of 1 kHz. The peak-to-peak change in the emitted current was 0.14 nA, which is 17.5 parts per million of the DC current with no laser. The change in the current is proportional to the power flux density at the tip, and measurements of the size of the focal spot and the optical power show that the power flux density was 7.09×106 W/m2 . Simulations suggest that approximately 23 of the observed change in the emitted current is caused by laser-induced heating, but the remaining 13 would be present at terahertz frequencies.