Direct quantitative imaging of the writing stage in a photosensitive azopolymer by digital holography

In this paper we demonstrate that the gradual formation of the surface relief grating (SRG) in azopolymer thin films under continuous light exposure can be directly observed in-situ and in real-time allowing full-field characterization with high-spatial resolution. We report here for the first time, at best of our knowledge, that digital holography (DH) can be adopted for investigating and monitoring inscribed holographic surface relief grating (SRG) of azopolymers by two-beam laser interference lithography over a wide area. The writing process can be assessed through Quantitative Phase Imaging (QPI). The reported results showing that the proposed method is a truly valuable diagnostic tool that could be useful for investigating the spatial distribution of the writing process that eventually could contribute to shedding light on the still unclear origin and related mechanism of SRGs formation in azopolymers.