Figure 3.

Emission wavelengths and the quadratic power-law dependence demonstrate unambiguous hyper-Rayleigh scattering (HRS) from the helicoids. (a) Emission spectrum of the l-helicoids dispersed in 1 mM aqueous cetrimonium bromide (CTAB) solution. Illumination was performed with left and right circularly polarized light (LCP and RCP, respectively) at the wavelengths (λ) of 730 and 788 nm. The dashed vertical lines indicate the HRS wavelengths corresponding to each λ. The wavelength error bars indicate the full-width at half-maximum (fwhm) of the transmission peak of the filters used. The detected signal at the HRS wavelengths is clearly above the multiphoton luminescence background. (b) Power dependence of the HRS intensity in spherical Au nanoparticles (NPs) (80 nm in diameter) suspended in water for LCP and RCP illumination at 730 nm. (c) Power dependence of the HRS intensity from core/shell helicoids with SiO₂ shell dispersed in 9:1 solution of 1 mM aqueous CTAB and ethanol, for LCP and RCP illumination with 720 nm light. (d) Power dependence of HRS from the solvent in which the helicoids were dispersed (1 mM aqueous CTAB), for LCP and RCP illumination at 720 nm. For figures (b), (c), and (d), the lines correspond to quadratic power-law fits.