Experimental Demonstration of Effective Medium Approximation Breakdown in Deeply Subwavelength All-Dielectric Multilayers

摘要

We experimentally demonstrate the effect of anomalous breakdown of theeffective medium approximation in all-dielectric deeply subwavelength thickness($d \sim\lambda/160-\lambda/30$) multilayers, as recently predictedtheoretically [H.H. Sheinfux et al., Phys. Rev. Lett. 113, 243901 (2014)].Multilayer stacks are composed of alternating alumina and titania layersfabricated using atomic layer deposition. For light incident on suchmultilayers at angles near the total internal reflection we observe pronounceddifferences in the reflectance spectra for structures with 10-nm versus 20-nmthick layers, as well as for structures with different layers ordering,contrary to the predictions of the effective medium approximation. Thereflectance difference can reach values up to 0.5, owing to the chosengeometrical configuration with an additional resonator layer employed for theenhancement of the effect. Our results are important for the development of newhigh-precision multilayer ellipsometry methods and schemes, as well as in abroad range of sensing applications.