Article

Local field asymmetry drives second-harmonic generation in noncentrosymmetric nanodimers. Nano Lett 7:1251-1255

Institute of Physics, Optics Laboratory, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland.
Nano Letters (Impact Factor: 13.59). 05/2007; 7(5):1251-5. DOI: 10.1021/nl0701253
Source: PubMed

ABSTRACT We demonstrate that second-harmonic generation (SHG) from arrays of non-centrosymmetric T-shaped gold nanodimers with a nanogap arises from asymmetry in the local fundamental field distribution and is not related strictly to nanogap size. Calculations show that the local field contains orthogonal polarization components not present in the exciting field, which yield the dominant SHG response. The strongest SHG responses occur through the local surface susceptibility of the particles for a fundamental field distributed asymmetrically at the particle perimeters. Weak responses result from more symmetric distributions despite high field enhancement in the nanogap. Nearly constant field enhancement persists for relatively large nanogap sizes.

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Available from: Brian K Canfield, Apr 01, 2015
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    • "Most experiments on SHG from metal surfaces have focused on the determination of the surface response [14] [15] [16] [17] [18]. The surface origin of the nonlinearity has also been implicated for the case of metal nanoparticles [19] [20] [21] and nanodimers [22]. The bulk effects have received much less attention in general, but have recently been used to model SHG from metal nanostructures [19] [20], including split-ring resonators [23]. "
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    ABSTRACT: New Journal of Physics Vol.12 Nr.6, 063009 Gold films of 20 and 150 nm nominal thickness were characterized by two-beam second-harmonic generation to address their second-order nonlinear optical responses of surface (dipolar) and bulk (higher multipolar) origin. The surface response is enhanced by ~20% in the case of the 20 nm film, as expected due to its higher surface roughness. Surprisingly, the bulk-type response is enhanced to a greater extent, exceeding 80%, and this can be explained by effective quadrupolar nonlinearity arising from the field interaction with the local nonlinearity of nanoscale surface features. Gold films of 20 and 150 nm nominal thickness were characterized by two-beam second-harmonic generation to address their second-order nonlinear optical responses of surface (dipolar) and bulk (higher multipolar) origin. The surface response is enhanced by ~20% in the case of the 20 nm film, as expected due to its higher surface roughness. Surprisingly, the bulk-type response is enhanced to a greater extent, exceeding 80%, and this can be explained by effective quadrupolar nonlinearity arising from the field interaction with the local nonlinearity of nanoscale surface features.
    New Journal of Physics 03/2010; 12:063009. DOI:10.1088/1367-2630/12/6/063009 · 3.67 Impact Factor
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    • "Extremely small nanoscale features, such as sharp tips or nanogaps between two particles, are expected to give rise to very strong local fields. The results for the T-shaped nanodimers with a varying gap size between the vertical and horizontal bars showed that the SHG signals exhibit peculiar dependence on the gap size [28]. These results were explained by the sensitive dependence of the polarized local-field distribution on the precise size of the nanogap. "
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    ABSTRACT: We review the state-of-the-art regarding the second-order nonlinear optical response of metal nanostructures and metamaterials. The present nanofab- rication of metal nanostructures gives rise to defects and other deviations from the ideal structure. Such factors may break the intended symmetry of the structure and give rise to nonlinear signals, which are ideally forbidden. Although second-order effects are electric-dipole-forbidden in the bulk of centrosymmetric materials, they become allowed through magnetic- dipole and electric-quadrupole effects. Improved understanding of the role of the surface and bulk effects in the second-order response of metals is needed in order to develop proper theoretical models for nonlinear metal nanostructures.
    Nonlinear Optics Quantum Optics 01/2010; 40:43-56.
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    • "To explain the CDR results, it is therefore sufficient to consider the distribution of the local field Y-component (Figure 6), which also has been shown to act as the main source of SHG [10]. In an ideal sample with no slant, the distributions for LCP and RCP are mirror images of each other (Figure 6a-d), because of the symmetry plane along the vertical bar. "
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    ABSTRACT: The mutual non-orthogonal orientations of its horizontal and vertical bars make T-shaped gold nanodimers chiral. Because of the broken symmetry second-harmonic generation from the structure has different efficiencies for left-and right-hand circularly-polarized fundamental light. The chiral signature arises from the coupling between the bars. One would therefore assume that the chiral signature is largest when the gap size is very small, because then the coupling is presumably the strongest. Counter-intuitively, the measurement results show a very small chiral signature for the smallest gap. To explain the results, one needs to consider the distribution of the local field in the unit cell of the structure.
    Proceedings of SPIE - The International Society for Optical Engineering 05/2008; DOI:10.1117/12.780513 · 0.20 Impact Factor
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