**5. Conclusion and outlook**

In this chapter, the interrelation of structure and function for volume holographic gratings was investigated with view to materials, methods and applications for volume holography. Hereby, volume holograms were considered as three‐dimensional optical structures with spe‐ cific functionality in terms of diffractive properties. The mechanism of volume holographic grating formation in photosensitive polymers was described. Specific requirements for vol‐ ume holographic materials and respective material systems were discussed. Different types of volume holographic gratings were characterized. Analytical methods for volume holograms were presented for the real‐time observation of grating formation as well as for the analysis of the final optical functionality. In addition, imaging techniques were discussed and opti‐ cal microscopy was applied to image 1D and 3D volume phase gratings. Lateral scanning was proposed to exploit the Gaussian intensity distribution of the recording beams, provid‐ ing direct access to the material response, based on a single exposure. Finally, some selected application areas have been described with respect to the specific advantages of volume holo‐ graphic materials for the respective applications. It could be demonstrated that the opening up of new applications for volume holography is accompanied with the design of novel, func‐ tionally tailored material systems. Therefore, a deeper understanding of volume holographic grating formation mechanisms remains required, driving the need for appropriate analytical methods. In this context, future opportunities and challenges related to the three dimension‐ ality of volume holographic gratings have been highlighted.
