The thermal response of a tunneling tip after illumination of the apex with
an ultrashort laser pulse of 1 ps duration is investigated. The finite ele
ment method is applied to calculate the resulting time-dependent temperatur
e distribution and the thermal expansion taking into account the elastic pr
operties of the tip material. The calculation reveals the three-dimensional
movement of the tip apex. The expansion of the tip occurs within a few nan
oseconds and after 10 mu s the tip has almost reached its original length a
gain. The bending of the tip due to the asymmetric illumination of the tip
occurs on the same time scale and is of the same order of magnitude as the
axial expansion. Under tunneling conditions the absolute magnitude of the e
xpansion can lead to the formation of nanocontacts. This accounts for the l
aser induced nanostructuring of surfaces that has been reported in literatu
re. The application of the thermal expansion as a fast switch for the tunne
ling current is proposed. (C) 2000 American Institute of Physics. [S0021-89
79(00)00504-1].