Simultaneous formation of holographic surface relief gratings and volume phase gratings in photosensitive polymer

ABSTRACT We report on secondary surface relief grating formation associated with holographic recording of volume phase gratings in epoxy-based, free-surface, volume holographic recording material, as well as in pure Epon SU-8 photoresist. Light-induced gratings are formed simultaneously by photo-triggered mass migration in the cause of component diffusion. Height profiles of surface relief gratings are compared with refractive index modulation profiles of corresponding volume phase gratings. Parasitic volume gratings and non-sinusoidal profiles are also investigated. Based on the correlation of volume and surface gratings, analysis of the height profiles allows conclusions to be drawn on the mechanisms of volume holographic grating formation. GRAPHICAL ABSTRACT IMPACT STATEMENT This paper reports on correlated volume and surface gratings, offering novel analytical possibilities to contribute to a deeper understanding of the holographic grating formation process