**6. Holographic recording in unpolarized light**

After passing of anisotropic or gyrotropic transparent objects, unpolarized light changes its statistical polarization structure. In this case the interaction with the initial reference wave gives interference pattern, which is modulated by intensity , as well as by polarization. Application of photosensitive material with Weigert's effect gives a possibility of holographic registration of above mentioned change of unpolarized light. For the verification of this assumption the corresponding holographic recording was carried out. As the simple anisotropic and gyrotropic objects can be use corresponding phase plates. It is also known that the interference pattern becomes to evenly lit if on the way of one of the interfering unpolarized waves put an anisotropic half-wave or gyrotropic half-wave (rotator at 900) phase plate (Langsdorf&Du Bridge, 1931; Vavilov, 1932). However, the polarization analysis shows that the total interference pattern is modulated with the polarization state. The optical scheme of holographic recording is shown in Fig. 25. The collimated beam of the He-Cd (*λ*=441.6 nm) by means of the Fresnel biprism **1** splits into two beams that overlaping in the plane of the photosensitive material **2**. Azo-dye doped gelatin was used as photosensitive material. On the way of one of the interfering wave the half-wave phase plate 3 was placed. The microlens **4** and the polarizer **5** allow to view the interference pattern and carry out its polarization analysis. In the absence of the half-wave phase plate, the interference pattern is modulated only by intensity, and its bright areas are also unpolarized (Fig. 26 **a**). After placing of the phase plate the modulation of interference pattern by the intensity disappears and it becomes uniformly illuminated (Fig. 26 **b**). However, the polarization analysis shows that the interference pattern is modulated with the polarization.

Fig. 25. The scheme of the holographic recording.

Fig. 26. Interference pattern of unpolarized light without (**a**) and with (**b**) *λ*/2 anisotropic phase plate.

After passing of anisotropic or gyrotropic transparent objects, unpolarized light changes its statistical polarization structure. In this case the interaction with the initial reference wave gives interference pattern, which is modulated by intensity , as well as by polarization. Application of photosensitive material with Weigert's effect gives a possibility of holographic registration of above mentioned change of unpolarized light. For the verification of this assumption the corresponding holographic recording was carried out. As the simple anisotropic and gyrotropic objects can be use corresponding phase plates. It is also known that the interference pattern becomes to evenly lit if on the way of one of the interfering unpolarized waves put an anisotropic half-wave or gyrotropic half-wave (rotator at 900) phase plate (Langsdorf&Du Bridge, 1931; Vavilov, 1932). However, the polarization analysis shows that the total interference pattern is modulated with the polarization state. The optical scheme of holographic recording is shown in Fig. 25. The collimated beam of the He-Cd (*λ*=441.6 nm) by means of the Fresnel biprism **1** splits into two beams that overlaping in the plane of the photosensitive material **2**. Azo-dye doped gelatin was used as photosensitive material. On the way of one of the interfering wave the half-wave phase plate 3 was placed. The microlens **4** and the polarizer **5** allow to view the interference pattern and carry out its polarization analysis. In the absence of the half-wave phase plate, the interference pattern is modulated only by intensity, and its bright areas are also unpolarized (Fig. 26 **a**). After placing of the phase plate the modulation of interference pattern by the intensity disappears and it becomes uniformly illuminated (Fig. 26 **b**). However, the polarization analysis shows that the interference pattern is modulated with the polarization.

**a b** Fig. 26. Interference pattern of unpolarized light without (**a**) and with (**b**) *λ*/2 anisotropic

**6. Holographic recording in unpolarized light** 

**1 2** 4 5

Fig. 25. The scheme of the holographic recording.

**3**

phase plate.

Fig. 27 shows the image of the interference pattern in three different orientation of the polarizer. Fig. 27 **a** shows the image of the interference pattern when the polarizer, is oriented along to the fast axis of the phase plate. Fig. 27 **b** shows the image of the interference pattern when the polarizer is oriented at the angle of 450 to the fast axis of the phase plate. Fig. 27 **c** shows the image of the interference pattern when the polarizer is oriented at the angle 900. From Fig. 27 **a** and **c** follows that there is a shift of the interference fringes as a result of changing the orientation of analyzer by 900. This testifies the existence in the interference pattern of two linear polarizations of orthogonal orientation. It is clear that under intermediate orientation of analyzer, the interference pattern will have uniform luminosity, which is confirmed by Fig. 27 **b**. Therefore, the ordinary photosensitive materials without Weigert's effect will not register such interference pattern. Thus, for realization of holographic recording in this case the application of the photosensitive material with Weigert's effect is necessary. The maximum of the diffraction efficiency of created holographic grating reached 10%. It is obviously that the greatest interest in this experiment represents comparison of polarization characteristics of the recorded object wave with that of the reconstructed wave. Investigation showed that reconstructed wave is also unpolarised. From this point of view is interesting to compare the statistical polarization structures of the wave formed with the help of half-wave plate and of its holographic reconstruction. For the comparison, the half-wave phase plate was removed. The object wave was blocked and with the help of micro lens **5** and polarizer **6**, the interference pattern between reconstructed and reference waves after hologram was observed. To obtain of equal intensities of interfering waves, in this case, the intensity of the reference wave was decreased with the help of a neutral light filter. The results of the investigation is presented in Fig. 28 **a,b, c**, which is practically identical to the results represented on Fig. 27 **a,b,c**.

Fig. 27. The interference pattern with *λ*/2 anisotropic phase plate after polarizer

Fig. 28. The interference with the reconstructed image of the *λ*/2 anisotropic phase plate after polarizer

Holography Based on the Weigert's Effect 143

with the help of unpolarized parts of interference pattern. The second part of isochrome is the result of holographic recording caused by influence of linearly polarized parts of interference pattern. This assumption is confirmed in Fig. 30 **c**. It represents the reconstructed image, when on the way of the reference wave, in the process of holographic recording, was placed a half-wave gyrotropic phase plate (quartz rotator 900), when the interference pattern consists of circularly and linearly polarized parts. Fig. 30 **c** shows picture only of the second part of isochromes, which is the result of holographic recording caused by influence of only linearly polarized parts of interference pattern. From the final result follows that, photosensitive material with the Weigert's effect can not register circularly polarized component of the interference pattern. Because of this we may conclude that to fully solve of this task of holography it is necessary to use a photosensitive

**a b c**

From the results described above it can be concluded that the holography based on the

7.1 Holographic recording and reconstruction of the polarization in some particular

7.2 Holographic recording and reconstruction of statistical polarization structure of

7.3 The possibility of creation of the holographic diffractive optical elements with

7.4 Some new processes (for example selfrecording) in the investigation of dynamic

7.5 Some new approaches in investigation of mechanisms of Weigert's effect in the Azo-

I would like to express my great love to my mother Neburishvili L.K., which helps me in all my life and express my gratitude to the late Professor Kakichashvili Sh.D. with whom I had

Fig. 30. The rceonstructed image of the strained transparent object.

Weigert's effect has the following advantages:

the privilege to work in the years 1982-1992.

anisotropic structure with advanced features.

processes of holographic recording based on the Weigert's effect.

Gabor, D. ( 1948). A New Microscope Principle, *Nature*, vol.161, pp. 777-778.

material with gyrotropic response.

**7. Conclusion** 

cases.

dyes.

**9. References** 

**8. Acknowledgment** 

unpolarized 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.

As noted above, if the unpolarized object wave is formed with the help of half-wave gyrotropic phase plate the interference pattern contains two mutually orthogonal circular polarization. In this case, when as a recording medium a photosensitive material with Weigert's effect is used, the holographic recording was impossible. Obtained results show that for holographic recording of full information about the wave scattered by the object, in general, Weigert's effect is insufficient and here is needed a photosensitive material with gyrotropic response.

In spite of this, the holographic recording in unpolarized light, extends considerably the possibilities of holography. One of the specific examples of the use of unpolarized light in holography is the solution to some problems of photoelasticity.

The holographic recording for strained transparent object was investigated experimentally, by means of unpolarized light. At the first stage of holographic recording, the photosensitive material was dichromated gelatin without the Weigert's effect. The reconstructed image is shown in Fig. 29 a. This image represents a picture of the isochromes. At the second stage, on the path of the reference wave the half-wave anisotropic phase plate was placed. The reconstructed image of the object, in this case, are represented in Fig 29 **b,c**. Fig. 29 **b** corresponds to holographic recording, when the optical axis of the phase plate is oriented vertically. Fig. 29 **c** corresponds to holographic recording, when the optical axis of the phase plate is oriented at an angle of 45 degrees to the vertical. These images represent the picture of the isochromes and isoclins. From Fig. 29 follows that, the reconstructed image contains some information about the distribution of anisotropy in the object. If on the way of reference wave is placed the half-wave girotopic phase plate (quartz rotator 900) the holographic recording does not take place in this photosensitive material.

Fig. 29. The rceonstructed image of the strained transparent object.

In the next stage of holographic recording, as a photosensitive material, was used azo-dye doped gelatin with Weigert's effect. The reconstructed images are represented in Fig. 30 **a,b,c** Fig.30 **a** correspond to the holographic recording without phase plate. In this case, the reconstructed image has practically an uniform illumination. Fig.30 **b** represents the reconstructed image when on the way of the reference wave, in the process of holographic recording, half-wave anisotropic phase plate was placed. Here is clearly observed the pattern of isochromes and isoclins. So, from Fig. 30 **a** and **b** follows that these images represent complementary images of isochromes and isoclins, which are shifted on the one lane relative to each other. The first part of isochrome is the result of holographic recording

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

As noted above, if the unpolarized object wave is formed with the help of half-wave gyrotropic phase plate the interference pattern contains two mutually orthogonal circular polarization. In this case, when as a recording medium a photosensitive material with Weigert's effect is used, the holographic recording was impossible. Obtained results show that for holographic recording of full information about the wave scattered by the object, in general, Weigert's effect is insufficient and here is needed a photosensitive material with

In spite of this, the holographic recording in unpolarized light, extends considerably the possibilities of holography. One of the specific examples of the use of unpolarized light in

The holographic recording for strained transparent object was investigated experimentally, by means of unpolarized light. At the first stage of holographic recording, the photosensitive material was dichromated gelatin without the Weigert's effect. The reconstructed image is shown in Fig. 29 a. This image represents a picture of the isochromes. At the second stage, on the path of the reference wave the half-wave anisotropic phase plate was placed. The reconstructed image of the object, in this case, are represented in Fig 29 **b,c**. Fig. 29 **b** corresponds to holographic recording, when the optical axis of the phase plate is oriented vertically. Fig. 29 **c** corresponds to holographic recording, when the optical axis of the phase plate is oriented at an angle of 45 degrees to the vertical. These images represent the picture of the isochromes and isoclins. From Fig. 29 follows that, the reconstructed image contains some information about the distribution of anisotropy in the object. If on the way of reference wave is placed the half-wave girotopic phase plate (quartz rotator 900) the

**a b c**

In the next stage of holographic recording, as a photosensitive material, was used azo-dye doped gelatin with Weigert's effect. The reconstructed images are represented in Fig. 30 **a,b,c** Fig.30 **a** correspond to the holographic recording without phase plate. In this case, the reconstructed image has practically an uniform illumination. Fig.30 **b** represents the reconstructed image when on the way of the reference wave, in the process of holographic recording, half-wave anisotropic phase plate was placed. Here is clearly observed the pattern of isochromes and isoclins. So, from Fig. 30 **a** and **b** follows that these images represent complementary images of isochromes and isoclins, which are shifted on the one lane relative to each other. The first part of isochrome is the result of holographic recording

polarization structure of unpolarized wave.

holography is the solution to some problems of photoelasticity.

holographic recording does not take place in this photosensitive material.

Fig. 29. The rceonstructed image of the strained transparent object.

gyrotropic response.

with the help of unpolarized parts of interference pattern. The second part of isochrome is the result of holographic recording caused by influence of linearly polarized parts of interference pattern. This assumption is confirmed in Fig. 30 **c**. It represents the reconstructed image, when on the way of the reference wave, in the process of holographic recording, was placed a half-wave gyrotropic phase plate (quartz rotator 900), when the interference pattern consists of circularly and linearly polarized parts. Fig. 30 **c** shows picture only of the second part of isochromes, which is the result of holographic recording caused by influence of only linearly polarized parts of interference pattern. From the final result follows that, photosensitive material with the Weigert's effect can not register circularly polarized component of the interference pattern. Because of this we may conclude that to fully solve of this task of holography it is necessary to use a photosensitive material with gyrotropic response.

Fig. 30. The rceonstructed image of the strained transparent object.
