**2.1 Basic requirements to recording media to construct static volume holograms**

The interest to static volume holograms with thickness of several millimeters is due, mainly, to their use in research and in creation of holographic optical elements (HOE) of various purposes with unique parameters (Sukhanov et al., 1984; Ludman at al., 1997; Popov, et al., 2000; Luo, at al., 2008). Requirements to materials for recording of such holograms are rather specific and cannot be met when using traditional light-sensitive materials.

Recording media for construction of static 3D-volume holograms should have the following properties:


Of greatest practical interest are media with photo-induced alteration of refractive index, which are suitable to record high-efficiency phase holograms, a special place among them belonging to media with latent image. Such media are most preferable in creation of HOE, as the recording process generates holograms of low efficiency, so-called "latent image" that leaves the recorded interference pattern undistorted. High efficiency of recorded holograms is in the case achieved through multiple magnification of modulation amplitude of a latent image hologram with the help of post-exposure treatment.

#### **2.2 The principle of composite structure**

The most natural way of realizing light-sensitive media with great physical thickness and high physical and mechanical performance is creation of medium-composite. The requisite set of parameters is in the case ensured by virtue of the medium components fulfilling different functions. Rigid framework has the necessary physical and mechanical properties and ensures the negligible shrinkage of samples; light-sensitive composite situated inside the framework ensures the properties needed for hologram construction (Sukhanov, 1991, 1994b).

The principle of creating the composite structure of light-sensitive medium by using a rigid framework was implemented in two ways. Firstly: the framework is created and formed independently; the light-sensitive composite is introduced into finished mold of the sample. The way was followed in realization of recording medium (RM) on the base of porous glasses with different light-sensitive composites (Sukhanov et al., 1988), one of them being the AgHal-based composite. Under such manner of RM realization, the framework effect on photochemical properties of samples is minimal and results from interaction of light-sensitive composite with the internal surface of the framework. Secondly: the framework is created and formed simultaneously with the light-sensitive composite – formation of sample-composite and rigid framework takes place at the same time. The manner was implemented by using organic dye phenanthrenequinone (PQ) as a light-sensitizing agent and forming the rigid framework by means of radical polymerization of composite on the base of methylmethacrylate monomer (MMA). The properties of the framework itself in such a RM are not limited only to maintenance of sample rigidity; the frame plays a certain part in recording, enhancement and fixation of holograms.
