**2.3 The dispersion refraction principle**

46 Holograms – Recording Materials and Applications

the relationship between physical-chemical processes of manufacturing technology for lightsensitive samples of volume recording medium and parameters of obtained holograms.

**2. Light-sensitive media for volume hologram recording: Basic requirements** 

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

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

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,

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

**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.

• high spatial resolution (greater than 3000 mm-1);

• sensitivity in the wavelength region of present-day lasers; • transparence at the operating wavelength (τ > 0.5); • non-destructive reconstruction of recorded information.

image hologram with the help of post-exposure treatment.

• large physical thickness (100-10000 μm); • high physical and mechanical performance;

**2.2 The principle of composite structure** 

**and principles of design** 

properties:

1994b).

The approach to creation of volume light-sensitive media, proposed in work (Lashkov & Sukhanov, 1978) and termed the dispersion refraction principle, consists in the following. It is necessary that the impact of light caused a sharp change of the absorption band of the material in the spectral region very far away from the operating wavelength range of recording radiation. The change of the absorption band is accompanied by change of dispersion, which leads to photo-induced refractive index appearing in the operating spectral range. Sensitivity of created RM in given wavelength interval can be ensured by using sensitized phototransformations. The change of refractive index due to the above causes was proposed to term as sensitized dispersion refraction. Purposeful use of given principle allows selecting substances with corresponding spectral parameters and calculating the possible modulation amplitude of constructed hologram. The principle became the base for realization of the first volume polymeric medium "Reoksan", whose light sensitivity is due to sensitized photo-oxidation of compounds of anthracene structure (Sukhanov, 1986, 1994a). It was used to create a medium with diffusion enhancement and is applicable to description and analysis of photophysical processes in most media intended for recording and reading the information in the optical spectral range.
