简介:Theplasmonicnanogapantennaisanefficientradiatingorreceivingopticaldevice.Theresonancebehaviorofopticalantennasiscommonlyattributedtotheexcitationofalocalizedsurfaceplasmonresonance(LSPR),whichcanbetheoreticallydefinedasthequasi-normalmode(QNM).ToclarifythephysicaloriginoftheLSPR,webuildupananalyticalmodeloftheLSPRbyconsideringamultiplescatteringprocessofpropagativesurfaceplasmonpolaritons(SPPs)ontheantennaarms.ThemodelcancomprehensivelyreproducethecomplexeigenfrequencyandthefielddistributionofQNMsoftheantenna,unveilingthattheLSPRarisesfromaFabry–PerotresonanceofSPPs.Byfurtherapplyingthecomplexpoleexpansiontheoremofmeromorphicfunctions,thefieldoftheantennaunderilluminationbyanearbydipoleemittercanbeanalyticallyexpandedwithQNMs,whichwellpredictsthefrequencyresponseoftheenhancementfactorofradiation.ThepresentmodelestablishesexplicitrelationsbetweentheconceptsoftheLSPRandthepropagativeSPPandintegratestheadvantagesoftheFabry–PerotandQNMformalismsofnanogapantennas.