Unlocked evanescent waves in periodic structures
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Updated: May 11, 2026

Evanescent Field Based Photoacoustics: Optical Property Evaluation at Surfaces
Published on: July 26, 2016
Muriel Botey1, Yu-Chieh Cheng, Vicent Romero-Garcia
1Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Urgell 187, Barcelona 08036, Spain. muriel.botey@upc.edu
Abstract:
We predict the existence of evanescent modes with unlocked phases in two-dimensional (2D) dielectric periodic structures. Contrary to what is known for one-dimensional structures, where evanescent fields lock to the host modulation, we show that in 2D systems a new class of evanescent modes exists with an unlocked real part of the wave vector. Hence, beams constructed from such unlocked evanescent waves can exhibit spatial effects. A significant focalization of a beam propagating within the band gap of a flat photonic crystal slab is also shown. The predicted phenomenon is expected to be generic for spatially modulated materials.
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