Microstructure of a reflection holographic grating inscribed in an absorptive azopolymer film

The microstructure of a reflection holographic grating fabricated via a photo-isomerization process in an absorptive azopolymer film is analyzed. A surface relief formation takes place on the film’s surface even in the reflection holographic configuration. The polarization-dependent diffraction efficiency and the polarization analysis reveal that the structure of the polarization grating inside the film strongly depends on the amount of optical absorption experienced by the two writing beams. A theoretical analysis shows that the reflection polarization grating, while mimicking a cholesteric liquid crystal structure, is composed of elliptic polarizations with the ellipticity going through a periodic modulation.