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The frequency of dipole relaxation of liquid crystal (LC) layer at LC-solid interface, f r , is shown to be in full correlation with the polar anchoring energy W p ; the increase of W p is accompanied with the decrease of f r . This correlation is established by the use of the aligning polyimide layers treated with different methods. The anchoring energy increases and the relaxation frequency decreases in the following sequence of processes: rubbing-photoalignment-plasma beam alignment. The correlation between W p and f r is an evidence of strong contribution of dipole-to-dipole interaction at the LC-substrate interface to polar anchoring of LC. Based on this correlation new method of polar anchoring measurement can be developed.

Abstract— We have developed an effective method for liquid‐crystal alignment of the large‐area substrates. This method is based on the oblique treatment of the alignment substrates with a “sheet” of accelerated plasma generated by the anode layer source of the “race track” geometry. During this treatment, the substrate or source is cyclically translated in the direction perpendicular to the plasma “sheet.” This method provides planar, tilted, and vertical liquid‐crystal alignment with excellent uniformity and reproducibility and easy axis control in the azimuthal and polar planes.

The ion adsorption=desorption processes initiated by LC filling in liquid crystal (LC) cells are studied. The LC we used was 5CB and the aligning substrates were UV irradiated polyvinylcinnamate (PVCN) films providing planar alignment of LC. It is shown that intensity of adsorption=desorption processes is strongly determined by purity of LC and irradiation associated parameters, such as exposure dose t exp and time period between irradiation and LC filling t fÀi . To fill the cells we used both 5CB kept in air and 5CB vacuumed at 10 À2 Torr over 1 h. The ion concentration in first portion of LC was estimated to be higher by factor 2 compared with the second one. The cell filling with LC kept in atmosphere is associated with intensive ion adsorption from LC bulk to aligning substrates (when exposure time is zero or when t fÀI > 1h) or with both adsorption and desorption of ions (in case when t fÀi ( 1h). In contrast, cell filling with vacuumed LC mainly initiates ions desorption from the polymer substrates. The latter effect is observed for non-irradiated cells too. This shows that even non-irradiated substrate charges, more likely by adsorption of air ions. The following UV irradiation just increases charging of aligning substrates.

Lasing in induced cholesteric liquid crystal (CLC) containing highly photosensitive azo chiral dopant (ChD) and pyrromethene laser dye was investigated. Due to the absence of excitation energy transfer from the dye molecules to the molecules of ChD in such a system, a low lasing threshold was achieved. When using violet and green lightemitting diodes, reversible frequency tuning was obtained in the range of about 30 nm with a tuning time 1-2 orders of magnitude smaller than in conventional CLC laser systems based on azo and azoxy photosensitive compounds. Further increase of the intensity of the excitation light by using a green laser pointer allowed us to achieve a record phototuning speed (∼21 nm in 148 ms).Distributed feedback (DFB) lasers based on dye-doped cholesteric liquid crystals (CLCs) were first established in 1980 [1]. Based on the characteristics reported to date, such as threshold excitation intensity, linewidth, and energy efficiency, they can actually be used for development of high-brightness laser displays [2]. Perfection of components for these devices, e.g., development of dye activators with minimal triplet-triplet absorption, CLCs with a high melting point and temperature-independent pitch length make it possible to produce lasing under continuous excitation [3].Since the creation of the DFB laser, a practical problem is to develop a method for tuning of its frequency, which would provide high speed and reversibility of this process. In practice, the tuning is achieved by changing the pitch of the CLC's helix, impacting on it by mechanical, thermal, electrical, or light factors [4]. The last process, photocontrolling of helical pitch, is of particular interest due to the remote, spatial, and temporal activation advantages of light stimulus. The method of tuning the lasing frequency based on this effect, which more generally is seen as a method of controlling light by means of light, is considered the most promising in terms of the above requirements of the process of tuning [4].Variation of the helical pitch under the influence of light is due to a change in the helical twisting power of chiral molecular switches in CLCs as a result of the photoconversion of molecules of the chiral dopant (ChD) [5-9], or liquid crystal host [10][11][12][13]. Often, these phototransformations (photo-Fries reaction, photolysis reaction, etc.) cause irreversible changes in the helical pitch [5,6]. However, some phototransformations (such as a trans-cis isomerization of azo and azoxy compounds) are generally reversible; the photoexcited cis isomers of such molecules relax to initial trans form when heated or exposed to light of a different wavelength. The case of cis-trans photoisomerization is the most interesting, because it allows one to change the frequency of lasing in two opposite directions by means of the same, quite a technological factor, i.e., light.Note that the efficiency of trans-cis and cis-trans photoisomerization and, consequently, the efficiency of lasing frequency tuning, depends on a number o...