Transformation Optics Description of Direct and Cascaded Third-Harmonic Generation

We analytically study the direct and cascaded third-harmonicgenerationfrom a nanowire dimer system with a transformation optics approach.The near-field, emission pattern, spectrum, and size dependence ofthe nanowire dimer are systematically explored. The calculation revealsthat the direct and cascaded third-harmonic generation possess differentmode excitations and size dependence for a plasmonic structure madeup of centrosymmetric media. We point out that these discrepanciescan be utilized as a fingerprint to clarify the nonlinear origin ofa measured third-harmonic signal. In addition, a broadband continuousmultiresonant state appears when the nanostructure becomes more singular,strongly improving the upconversion efficiency.

Automated summary

We analytically study the direct and cascaded third-harmonic generation from a nanowire dimer system with a transformation optics approach. The near-field, emission pattern, spectrum, and size dependence of the nanowire dimer are systematically explored. The calculation reveals that the direct and cascaded third-harmonic generation possess different mode excitations and size dependence for a plasmonic structure made up of centrosymmetric media. We point out that these discrepancies can be utilized as a fingerprint to clarify the nonlinear origin of a measured third-harmonic signal. In addition, a broadband continuous multiresonant state appears when the nanostructure becomes more singular, strongly improving the upconversion efficiency.