Intermittency in second-harmonic radiation from plasmonic hot spots on rough silver films

Surface enhancement of electromagnetic fields in plasmonic hot spots formed on rough silver films enables the observation of second-harmonic generation (SHG) from single metal nanoparticles. Nonlinear light scattering from these particles exhibits blinking in analogy to luminescence from single quantum dots, molecules and atoms; and fluctuations in single molecule surface-enhanced Raman scattering. Hot spots also display multiphoton white light emission besides SHG. In contrast to SHG, white light emission is stable with time, demonstrating that it is not the plasmonic field enhancement which fluctuates but the nonlinear polarizability (χ⁽²⁾) of the emitting species.