**Author details**

sharply on close‐up and distant objects) or brightness‐darkness adaptation. With regard to the design, diffractive approaches are feasible and highly favorable in many respects com‐ pared with conventional refractive designs [57, 58]. Systems currently in use are limited to surface patterns, providing combined diffractive‐refractive structures. Volume holographic systems, with potential special features involved, have not yet been applied. However, the use of refractive‐diffractive optical properties by means of an integration of volume structuring, in combination with surface modification could provide highest possible functionality and applicability. Besides design, performance and functionality, biocompatibility, especially in case of foldable hydrogel lenses, must be ensured [59, 60]. Prospective IOLs could fulfill their function with an optically structured volume, leaving the surface free for other functionalities. Thus, late postoperative opacification of implanted lenses, resulting in glare and misty vision, might be addressed based on surface modifications for specific bio‐interaction [60]. In any case, the integration of optical functionality into the volume of intra‐ocular lenses might suc‐ ceed according to the leading idea *from structure to function* and would be accompanied with

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‐

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research

considerable benefits.

**Acknowledgements**

**5. Conclusion and outlook**

20 Holographic Materials and Optical Systems

ality of volume holographic gratings have been highlighted.

Foundation) under grant number SA 2990/1‐1.

Tina Sabel\* and Marga C. Lensen

\*Address all correspondence to: tina@physik.tu‐berlin.de

Department of Chemistry, Technische Universität Berlin, Berlin, Germany
