  We have investigated field emission patterns from a clean tungsten tip apex
induced by femtosecond laser pulses. Strongly asymmetric modulations of the
field emission intensity distributions are observed depending on the
polarization of the light and the laser incidence direction relative to the
azimuthal orientation of tip apex. In effect, we have realized an ultrafast
pulsed field-emission source with site selectivity on the 10 nm scale.
Simulations of local fields on the tip apex and of electron emission patterns
based on photo-excited nonequilibrium electron distributions explain our
observations quantitatively.
