Calculation of the field enhancement on laser-illuminated scanning probe tips by the boundary element method

In the near field of an illuminated scanning probe tip with a dimension much smaller than a light wavelength a tremendous field enhancement is possible. This effect is similar to field enhancement on small metal particles first investigated in SERS (surface-enhanced Raman spectroscopy). In this article we propose to apply the boundary element method (BEM) to calculate the electric potential and field for an arbitrary tip-sample geometry, BEM works especially well for the Laplace problem with piecewise constant material properties. We developed a simple and fast program and carried out calculations for some tip-sample configurations.