Spatial anticorrelation between nonlinear white-light generation and single molecule surface-enhanced Raman scattering.

We investigate the correlation between plasmon-enhanced nonlinear white-light emission and single-molecule surface-enhanced Raman scattering (SERS) on fractal silver films using a conjugated polymer as a versatile analyte. Single molecule resonance SERS is preferentially observed from sample positions which do not exhibit nonlinear light emission under infrared excitation. The results suggest that the broad emission background often associated with single molecule SERS may not be intrinsic to the huge optical field amplifications characteristic of SERS. The two-photon imaging technique promises to offer a facile approach to prescreen substrates for their single molecule SERS capability.