Abstract
ABSTRACTWe 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.
Highlights
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
Some systems have been described for hybrid volume/surface gratings, where a periodic modulation of the surface is observed in addition to a volume phase grating [1–3]
Permanent volume gratings with high diffraction efficiency are formed in the epoxy-based volume holographic recording material, while only transient volume gratings are formed in the pure SU-8, with very low permanent diffraction efficiency [17]
Summary
Diffractive structures can be found on the surface as well as in the volume of optical materials. Corresponding representatives are surface relief gratings (SRGs) and volume phase gratings (VPGs), respectively Both can be light induced, e.g. by means of holographic recording, but they differ fundamentally in the mechanism of the diffraction of light, as well as regarding their particular characteristics such as achievable diffraction efficiency and, as a consequence, with regard to their specific applications. Some systems have been described for hybrid volume/surface gratings, where a periodic modulation of the surface is observed in addition to a volume phase grating [1–3] Such dual grating structures are of exceptional interest for many applications such as the fabrication of diffractive solar concentrators [4], for protective technologies [3,5] or for multi-functional optical systems as tailor-made diffractive devices, for example, for enhanced multilevel security or integrated optics [6], as well as for biomaterials such as for novel intraocular lenses (IOLs) [7]
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