Bound-states-in-the-continuum (BIC) is an emerging concept in nanophotonics with potential impact in applications, such as hyperspectral imaging, mirror-less lasing, and nonlinear harmonic generation. As true BIC modes are non-radiative, they cannot be excited by using propagating light to investigate their optical characteristics. In this paper, for the 1st time, we map out the strong near-field localization of the true BIC resonance on arrays of silicon nanoantennas, via electron energy loss spectroscopy with a sub-1-nm electron beam. By systematically breaking the designed antenna symmetry, emissive quasi-BIC resonances become visible. This gives a unique experimental tool to determine the coherent interaction length, which we show to require at least six neighboring antenna elements. More importantly, we demonstrate that quasi-BIC resonances are able to enhance localized light emission via the Purcell effect by at least 60 times, as compared to unpatterned silicon. This work is expected to enable practical applications of designed, ultra-compact BIC antennas such as for the controlled, localized excitation of quantum emitters.

Zhaogang Dong;Zackaria Mahfoud;Ramón Paniagua-Domínguez;Hongtao Wang;Antonio I.Fernández-Domínguez;Sergey Gorelik;Son Tung Ha;Febiana Tjiptoharsono;Arseniy I.Kuznetsov;Michel Bosman;Joel K.W.Yang

Institute of Materials Research and Engineering,A*STAR(Agency for Science,Technology and Research),2 Fusionopolis Way,#08-03 Innovis,138634 Singapore,Singapore;Department of Materials Science and Engineering,National University of Singapore,9 Engineering Drive 1,117575 Singapore,Singapore;Singapore University of Technology and Design,8 Somapah Road,487372 Singapore,Singapore;Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center,Universidad Autónoma de Madrid,28049 Madrid,Spain;Singapore Institute of Food and Biotechnology Innovation,A*STAR(Agency for Science,Technology and Research),31 Biopolis Way,#01-02 Nanos,138669 Singapore,Singapore

光：科学与应用（英文版）

[1]Zhaogang Dong;Zackaria Mahfoud;Ramón Paniagua-Domínguez;Hongtao Wang;Antonio I.Fernández-Domínguez;Sergey Gorelik;Son Tung Ha;Febiana Tjiptoharsono;Arseniy I.Kuznetsov;Michel Bosman;Joel K.W.Yang-.Nanoscale mapping of optically inaccessible bound-states-in-the-continuum)[J].光：科学与应用（英文版）,2022(02):188-196

unpatterned

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