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The optical second harmonic (SH) response from gold metallic nanocylinders with diameters of 80 and 120 nm arranged in hexagonal arrays has been determined as a function of the input fundamental polarization angle for the on- and off-axis transmission geometries and crossed output polarization configurations. For the on-axis transmission geometry, the nonlinear response of the nanocylinders is shown to be mainly incoherent, of pure electric dipole nature and arising from the breaking of the centrosymmetric shape of the body of the cylinders in a plane parallel to the substrate surface. Small angle off-axis experiments however show that the coherent contribution to the nonlinear response is size dependent suggesting that, besides the out-of-plane nonlinearity, retardation effects may also play a nonnegligible role. [ABSTRACT FROM AUTHOR]

Hyper Raleigh scattering, a common technique to investigate the second harmonic light scattered from a liquid suspension of molecular compounds and to determine their quadratic hyperpolarizability, has been used for aqueous suspensions of gold nanoparticles, the diameter of which ranges from 20 up to 150 nm. The hyper Rayleigh signal intensity was recorded as a function of the angle of polarization of the incident fundamental wave. For the particles with a diameter smaller than 50 nm, the response is dominated by the dipolar contribution arising from the deviation of the particle shape from that of a perfect sphere. For larger diameter particles, retardation effects in the interaction of the electromagnetic fields with the particles cannot be neglected any longer and the response deviates from the pure dipolar response, exhibiting a strong quadrupolar contribution. It is then shown that in order to quantify the relative magnitude of these two dipolar and quadrupolar contributions, a weighting parameter ζV which equals unity for a pure quadrupolar contribution and vanishes for a pure dipolar response, can be introduced. [ABSTRACT FROM AUTHOR]

Very high-lying vibrational levels of the 1[SUBg] ∼ 1 II[SUBg] electronic state of K[SUB2] have been observed in a photoassociation experiment using an ion detection scheme. The photoassociation measurements have been treated together with laser induced fluorescence data recorded by Fourier transform spectrometry to construct a pointwise potential curve for this electronic state. Several vibrational levels were observed by both techniques, so the dissocation energy can be deduced without extrapolation, from the sum of binding energies measured in photoassociation and vibrational energies established with respect to the potential minimum (defined by the fluorescence data), giving D[SUBe] = 1290.292 ± 0.002 cm[SUP-1] (1 standard deviation.) The potential curve reproduces over 2000 term values (up to v = 138) with a root mean square error of 0.0025 cm[SUP-1]. Nevertheless, small differences are found between the rotational constants generated from the potential curve and the effective rotational constants deduced from binding energy measurements at very high v. The smoothness of the outermost part of the pointwise potential energy curve has been investigated through fits to a Hund's case (c) asymptotic model. [ABSTRACT FROM AUTHOR]

The resonance effects on the optical second-harmonic generation from 140-nm silver nanoparticles is studied experimentally by hyper-Rayleigh scattering and numerically by finite element method calculations. We find that the interferences between the broad dipolar and narrow octupolar surface plasmon resonances leads to nonlinear Fano profiles that can be externally controlled by the incident polarization angle. These profiles are responsible for the plasmon-induced suppression of the second harmonic generation. [ABSTRACT FROM AUTHOR]