title: Observation of sub-Bragg diffraction of waves in crystals.
abstract: We investigate the diffraction conditions and associated formation of stop gaps for waves in crystals with different Bravais lattices. We identify a prominent stop gap in high-symmetry directions that occurs at a frequency below the ubiquitous first-order Bragg condition. This sub-Bragg-diffraction condition is demonstrated by reflectance spectroscopy on two-dimensional photonic crystals with a centered rectangular lattice, revealing prominent diffraction peaks for both the sub-Bragg and first-order Bragg conditions. These results have implications for wave propagation in 2 of the 5 two-dimensional Bravais lattices and 7 out of 14 three-dimensional Bravais lattices, such as centered rectangular, triangular, hexagonal, and body-centered cubic.
authors.affiliation: Complex Photonic Systems (COPS), MESA + Institute for Nanotechnology, University of Twente, Enschede, The Netherlands. s.r.huisman@utwente.nl
authors.forename: Simon R
authors.initials: SR
authors.lastname: Huisman
authors.forename: Rajesh V
authors.initials: RV
authors.lastname: Nair
authors.forename: Alex
authors.initials: A
authors.lastname: Hartsuiker
authors.forename: Léon A
authors.initials: LA
authors.lastname: Woldering
authors.forename: Allard P
authors.initials: AP
authors.lastname: Mosk
authors.forename: Willem L
authors.initials: WL
authors.lastname: Vos