Saturation and Reverse Saturation of Scattering

We report that backscattering from an isolated gold nanoparticle exhibits not only saturation, but also reverse saturation. Wavelength-dependent and intensity-dependent studies reveal that nonlinear scattering is dominated by SPR and shares a similar physical origin with nonlinear absorption. The reversibility and repeatability of saturable scattering (SS) and reverse saturable scattering (RSS) are validated via repetitive excitation on the same set of particles. Compared to fluorescence, our novel discovery of single-particle-based SS and RSS does not suffer from bleaching and can be used as a more robust contrast agent for optical microscopy. Under a reflection confocal microscope, interesting point-spread functions are observed, with full-width-of-half-maximum of central and side lobes reduced to λ/5 and λ/13, showing great potential for superresolution microscopy.

S. W. Chu, H. Y. Wu, Y. T. Huang, T. Su, H. Lee, Y. Yonemaru, M. Yamanaka, R. Oketani, S. Kawata, S. Shoji, and K. Fujita, "Saturation and Reverse Saturation of Scattering in a Single Plasmonic Nanoparticle," Acs Photonics 1, 32-37 (2014).