Exploration On The Real-time Holographic Properties Of Liquidcrystal Cell Based On The Photoconductive ZnSe Film

In recent years, dynamic holographic 3D display technology has continuously attracted great attention, which covers a wide range of applications, such as great-potential display industry in commercial, training simulation in military and dynamic monitoring in medical. Improving the response speed of optically holographic recording material based on liquid crystal soft material has a far-reaching significance. This dissertation aims at shortening response time further after achieving as short as 17.1 ms response time in our group. Thorough analyzing photorefractive effect in 5CB material, we seek possible reasons that limit response speed, and hence to optimize the structure of LC cell and the condition of experiments. For this purpose, we designed and fabricated eight sandwich-structured LC cells with different thickness, with photoconducting ZnSe films, and studied holographic recording and other properties systematically.The two-beam coupling(2BC) experiments with eight samples revealed that the thinner the LC layer is, the larger the exponential gain coefficients(EGCs) is. Particularly, the EGCs of the thinnest sample 3.5 μm reached 1795.0 cm-1. After we analyzed, it seems the high EGCs behind the thin sample attributed to two reasons: one is the surface-mediated effect, the other is the thickness d of LC layer. First, in the relatively thin LC cells, surface-mediated effect dominated. Second, although the net gains are comparable for various samples, only net gain being divided by d can we obtain the EGCs according to the EGCs calculating formula. Therefore, a thinner d would result in a higher EGC.It was shown that 6.4 μm sample possesses the fastest response speed as to be 5.4 ms(about 200 frames per second) from grating read-out experiments. This makes it possible to truly implement quasi real-time holographic dynamic display. Combining the experimental result with the theoretical analysis, we concluded that for 6.4 μm sample the surface-mediated effect and volume effect was coincidently complementary. The thinner a sample is, the less the freedom of LC molecules is within it. Oppositely, the thicker is the sample, the longer time it needs to transport charge carriers. Besides, under the same applied field needed for fastest response, the first-order diffraction efficiency in 6.4 μm sample still needs to be improved further, with only 2.6%. Also, there exerted a similar rule among different samples. The thicker one has a higher maximum diffraction efficiency.Generally, diffraction patterns among most samples are one-dimensional. Exceptionally, pattern diffracted from 31.0 μm sample came to be two-dimensional in both 2BC and grating read-out experiments. Taking a deeper analysis on the set-up, we found that the diffraction belongs to Fraunhofer diffraction due to the distance issue between diffraction pattern and grating. That means, the inverse Fourier transform of the pattern would come into the transmittance function of grating. Calculation and simulation showed that the grating morphology formed in 31.0 μm sample is also two-dimensional.