Bragg Selectivity of Thick Holograms

Bragg selectivity is a fundamental physical property of thick-emulsion volume holograms. As the thickness of the recording medium increases, the system becomes highly selective about the angles and wavelengths of illumination.

This selectivity is governed by Bragg’s diffraction equations. When light enters the thick hologram, hundreds of micro-refractive layers must align to reflect a coherent wave. Deviations in illumination angle or wavelength dismantle this constructive feedback.

This sensitivity allows thick holograms to act as high-efficiency wavelength filters. They reflect crisp, monochromatic images under white light while letting other wavelengths pass, providing a key mechanism for advanced security foils.