ABSTRACT
Field enhancements are best observed by exploiting nonlinear optical e˜ects such as second-harmonic generation (SHG) (Smolyaninov et al. 1997, 2000, Jakubczyk et al. 1999, Zayats et al. 2000, Shen et al. 2001, Biagioni et al. 2007, Breit et al. 2007)
or two-photon photo-luminescence (TPPL) (Jakubczyk et al. 1999, Bouhelier et al. 2003, 2005, Imura et al. 2005, 2006), which depend on the square of the light intensity, thus amplifying local œeld variations. To observe a signiœcant nonlinear response, the samples are typically illuminated by high peak intensities, such as those associated with ultrashort laser pulses. Nonlinear optical microscopies, either in the far œeld or in the near œeld, are thus becoming powerful tools for the study of nanoscale œeld enhancements.
