Nanoscale nonlinear optical process: theoretical modeling of second-harmonic generation for both forbidden and allowed light

Based on a combination of the multiple-multipole method and nonlinear coupl ed-wave equations, a rigorous three-dimensional numerical simulation of non linear optical interactions between an optical near field and a nonlinear m edium is performed, allowing us to study the dependence of second-harmonic (SH) nearfield intensity on tip-sample distance and the polarization state of the incident fundamental wave. It is demonstrated that allowed and forbi dden Light make different contributions to the SH near-field intensity. (C) 2000 Optical Society of America.