Weigert’s effect

From the point of view of Weigert s effect the azo-dyes can be considered as the most interesting materials because of their photosensitivity, reversibility and high value of photo anisotropy (Kondo, 1932). The Azo-dyes are the organic compounds containing one or more group of double chemical bonds of nitrogen, the so called — N = N — chromophore. 

Analogous transformation will have more complex nature for the azo-dyes containing more than one — N = N — chromophore and different radicals. Currently it is accepted, that the basic factor of Weigert s effect is photo E/Z isomerization in azo-dye materials. But, it is proved, that E/Z isomerization is not necessary and sufficient requirement process for the initiation of Weigert s effect in the azo-dye materials and its mechanisms may be different. Some authors attempted to explain Weigert s effect in the azo-dye materials, but they were not confirmed uniquely (Shatalin, 1989 Ebralidze, 2002). 

The Azo-dyes are the most promising photosensitive materials with the Weigert s effect. 

From this point of view azo-dye materials with Weigert s effect have obvious... 

One more possible mechanism of the Weigert s effect in azo-dye colored materials... 

The increase of the absorption in the wave range of 400 - 560 nm as a result of the influence of the actinic light confirms E/Z isomerization, the sole possible photo-process in this instance. Weigert s effect does not take place in the given case. Consequently, the E/Z photoisomerisation is not sufficient condition for it s emergence. The water-soluble Azodyes Fernandes and Mordant Pure Yellow were introduced into gelatin. Fig. 2 shows spectral transmittance characteristics of azo-dye Mordant Pure Yellow before (curve I) and after (curves 11,111,1V) exposure to linearly polarized actinic light (A = 441,6 nm). 

Fig. 4. The scheme of multiple recording and erasure of Weigert s effect...

An interesting result gives the investigation of holographic recording in the azo-dye material with Weigert s effect in the general case of linear polarization of the object waves. For the simple theoretical calculations the Jones vector-matrix method of was used (Jones, 1941 Kakichashvili, 1974). 

Photosensitive material H with Weigert s effect perpendicular to axis OZ is placed into a rectangular system of coordinates (Fig. 7). 

This is the imaginary image of the object which preserves both the polarizing character and direction of the object wave. Thus, the theory shows the possibility of the holographic recording and adequate reconstruction of linear polarization in general case on the basis of the Weigert s effect. 

Selection of the optimal absorption of the azo-dye with Weigert s effect. 

Clearly, if such a wave is created in a photosensitive material with the Weigert s effect, the obtained picture of the anisotropy will have a chiral structure, similar to the cholesteric... 

A=488.0 nm and A=514.5 nm), the polarization in the interference pattern is near to linear. In addition, the intensity of the interference pattern, in the photosensitive layer, in this case, will be higher, and thus the result of the Weigert s effect will be also larger. Accordingly, the diffraction efficiency of such structure may reach higher values. 

Fig. 23. The schematic picture of creation of the Weigert s effect by the linearly polarized (a) and elliptically polarized (b) light.

These results confirm that holographic recording in the unpolarized light, on the basis of Weigert s effect, when the object wave is forming with the help of half-wave anisotropic phase plate, gives a possibility of the adequate reconstruction of the changing of statistical polarization structure of unpolarized wave. 

---