Abstract
We investigated the optical third harmonic generation (THG) signal from nanostructure-covered microcubes on Ni. We found that the hierarchical structures greatly change the third-order optical nonlinearity of the metallic surface. While the symmetry and lightning rod (LR) effects on microstructures did not significantly influence the THG, the localized surface plasmon (LSP) effect on the nanostructures enhanced it. By removing the nanostructures on the hierarchical structures, THG intensity could be strongly suppressed. In the present paper, we also discuss the mechanism that enhances THG in nano/micro structures.
Highlights
Optical third harmonic generation (THG) is a complicated coherent nonlinear optical process [1].In general, nonlinear waves are forbidden for centrosymmetric systems [1,2,3,4]
The coordinate system is oriented so that the x and y coordinates are in the plane and the z coordinate is in the direction normal to the substrate surface [14]
Equation (1) expresses that the s-polarized THG intensity |Es (3ω)|2 depends on the nonlinear susceptibility χ and the y-directed local field EY,loc of the electric field component
Summary
Optical third harmonic generation (THG) is a complicated coherent nonlinear optical process [1].In general, nonlinear waves are forbidden for centrosymmetric systems [1,2,3,4]. Optical third harmonic generation (THG) is a complicated coherent nonlinear optical process [1]. THG processes are useful for various applications, such as autocorrelators [5] and nonlinear imaging [6]. The enhancement of THG responses by surface plasmons (SPs) has been reported among many researchers [7,8,9]. Since THG intensity is proportional to the third power of the incident light intensity [1], the SP-assisted electric field enhancement at the surface areas greatly enhances THG light strength. The magnitude of this enhancement is different from that of optical second harmonic generation (SHG)
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