Optical anisotropy, films

Wetzel, R., Zirwer, D., Becker, M. Optical anisotropy of oriented deoxyribonucleic acid films of diffi-rcrit water content. Biopolymers 8 (1969) 391-401... 

It is important to emphasize that the above discussion does not take into account the optical anisotropy of the oriented films (5), and assuming the same refractive index for all the sample. However, if the films have the same molecular density, such as, for the first approximation, complete monolayers (5-7), these constraints are not critical. On the other hand, these considerations may be important in partial monolayers, since significant deviations may arise when going down in surface concentration. The refractive index of the film, n2, is a monotonic function of the molecular density, varying from 1.00, in the limit of zero surface coverage, to about 1.50, in a complete closely-packed monolayer. 

Before and after the works described above, contributions to the design and fabrication of similar multicomponent films or gels of cholesteric character, mainly based on HPC, EC, or their derivatives were also made [202, 219-224], Some of these [219,220,224] dealt with shear-deformed network systems preserving a unique banded structure, so that the disappearance and recovery of the optical anisotropy could be controlled thermo-reversibly. Special mention should be made of the successful preparation of two novel classes of solid materials maintaining cholesteric liquid-crystalline order. One consists of essentially pure cellulose only, and the other is a ceramic silica with an imprint of cellulosic chiral mesomorphy. 

When optical anisotropies form spontaneously in the polymeric film during deposition, the situation is more complicated. Significant effects are observed in optical and spectroscopic properties, such as LED emission [17] and waveguide propagation [45-50,52,64], For these films, accurate evaluation of the optical constants is more difficult and must be based on variable incidence angle measurements, as in the case of surface plasmon resonance [45-47], waveguide propagation [48-50,52], ellipsometry [64,67], and reflectance/transmittance [68]. 

Single crystal ZnO films have a strong optical anisotropy and can be used for modulation of UV radiation. ZnO modulators with a contrast of 70 1 and an operation speed of 100 ps have been designed already. ... 

Blinov, L. M., Barberi, R., Kozlovsky, M. V., Lazarev, V. V., and de Santo, M. P. Optical anisotropy and four possible orientations of a nematic liquid crystal on the same film of a photochromic chiral smectic polymer. / Nonlinear Opt. Phys. Mat. 9, 1 (2000). 

Illumination of LBK films of copolymers 34 (1 2.4) in the liquid crystalline state at 63"C, with polarized light at 457 nm, results in a photo-induced optical anisotropy. That is, the chromopbores can be reoriented, which indicates that efficient photoisomerization is possible. Photoreorientation is also possible at room temperature after the original structure of the LBK film has been broken up by irradiation with UV light (that is, after a photostationary state with a high content of c -isomer has been established). ... 

Palto, S. P., Makhete, J., Germain, C., and Durand, G. On the Nature of Wiotoinduced Optical Anisotropy in Diacetylene Langmuir-Blodgett Films. Mol. Cryst. Liq. Cryst. 282, 451 (1996). 

T. Fischer, L. Lasker, J. Stumpe, and S. G. Kostromin, Photoinduced optical anisotropy in films of photochromic liquid crystalline polymers, Photochem. Photobiol. A 80, 453 159... 

L. Lasker, T. Fischer, J. Stumpe, and R. Ruhmann, Optical anisotropy in amorphous films of photochromic polymers due to photochemical ly induced orientational order, J. Inf. Rec. Matter. 21, 635-638 (1994). 

Before proceeding with discussion of the measurement of birefringence of a fiber it should be pointed out that if biaxial orientation exists in a film all three birefringence values must be determined to characterize the optical anisotropy. 

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