A comparative analysis of surface and bulk contributions to second-harmonic generation in centrosymmetric nanoparticles

Daniel Timbrell,Yuri S Kivshar,Jian Wei You,Nicolae C Panoiu

doi:10.1038/s41598-018-21850-8

Daniel Timbrell, Yuri S Kivshar + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-21850-8

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Abstract

Second-harmonic generation (SHG) from nanoparticles made of centrosymmetric materials provides an effective tool to characterize many important properties of photonic structures at the subwavelength scale. Here we study the relative contribution of surface and bulk effects to SHG for plasmonic and dielectric nanostructures made of centrosymmetric materials in both dispersive and non-dispersive regimes. Our calculations of the far-fields generated by the nonlinear surface and bulk currents reveal that the size of the nanoparticle strongly influences the amount and relative contributions of the surface and bulk SHG effects. Importantly, our study reveals that, whereas for plasmonic nanoparticles the surface contribution is always dominant, the bulk and surface SHG effects can become comparable for dielectric nanoparticles, and thus they both should be taken into account when analyzing nonlinear optical properties of all-dielectric nanostructures.

Highlights

The strong field enhancement that accompanies the excitation of surface-plasmon polaritons (SPPs) on metallic nanoparticles[1,2] makes these nanostructures ideal candidates for many applications, including nanoscale antennae, single-molecule detection via surface-enhanced Raman scattering, metallic nanotips for near-field optical microscopy, and optically-active guiding nanostructures[3,4,5,6,7,8,9]
As in the linear case, these strong nonlinear optical effects in plasmonic structures are accompanied by large optical losses, which restrict the range of applications to which nonlinear optical interactions can be employed
Our analysis suggests that it is conceivable that, at least in the case of all-dielectric nanoparticles, one can design structures for which the bulk effects are comparable or even larger than the surface ones. This means that care must be taken when experimental results pertaining to second-harmonic generation (SHG) in all-dielectric nanostructures made of centrosymmetric materials are theoretically interpreted, as our analysis suggests that the validity of the commonly used practice to neglect the bulk contribution to SHG might break down in this instance

Summary

Model and scattering configuration

One expects that the ratio between the contribution of bulk and surface effects to SHG is primarily determined by the inhomogeneity of the optical near-field at the FF, an effect that is more predominant at the nanoparticle resonances This inhomogeneity is the largest at the wavelengths of the resonances of the particle, and does not change significantly with the angle of incidence. Electromagnetic multipoles associated to a nanoparticle can reveal key physical insights into the optical properties of the scatterer[47] For both types of crosses, we performed a multipole decomposition, whereby the radiated powers associated with the first three terms of the multipole expansion were calculated.

Total Electric Dipole

Results and Discussion

Conclusion

Additional Information