Whispering-gallery modes promote enhanced optical backflow in a perforated dielectric microsphere

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Abstract
Optical energy flow inside a dielectric microsphere is usually co-directed with the optical wave vector. At the same time, if the optical field in a microsphere is in resonance with one of the high-quality spatial eigenmodes (whispering-gallery modes— WGMs), a region of reverse energy flow emerges in the shadow hemisphere. This area is of considerable practical interest due to increased optical trapping potential. In this Letter, we consider a perforated microsphere with an air-filled pinhole fabricated along the particle diameter and numerically analyze the peculiarities of WGM excitation in a nanostructured microsphere. A pinhole isolates the energy backflow region of a resonant mode and changes a perforated microsphere into an efficient optical tweezer. For the first time, to the best of our knowledge, a multiple enhancement of the energy backflow intensity in the pinhole at a WGM resonance is revealed and we discuss the ways for its manipulation.
Funding Information
  • Ministry of Science and Higher Education of the Russian Federation
  • Tomsk Polytechnic University

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