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We have investigated two-dimensional anisotropic gratings in photocrosslinkable polymer liquid crystals irradiated with three mutually coherent beams. Both birefringence and surface topological modulation were induced by reorientation and migration of mesogenic molecules. Atomic force microscopy reveals a close-packed hexagonal array of gratings fo...
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... this study, we used a photocrosslinkable poly(metha- crylate) liquid crystal with 4-(4-methoxycinnamoyloxy)bi- phenyl side groups. The structure of the PPLC is shown in Fig. 3. The polymer film was prepared by spin casting a solution of the PPLC in methylene chloride on a quartz substrate. The thickness of the PPLC film was about 100 nm. The direction of orientation of the mesogenic molecules in the resultant PPLC film was random, and the film was transparent prior to annealing. Under linearly-polarized UV ...
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... When a plane beam is incident to the monolithic gratings, the first-order diffractions of each grating cross at the same angles in the interference plane, as shown in Fig. 1(b). This type of multi-beam interferometry is usually used for fabricating periodic structures [25][26][27]. ...
... The interference field of three circularly polarized beams was calculated as described in Section 2 [27,30]. Figure 3(a) shows how the intensities I 12 , I 23 , and I 13 depend on the anisotropic phase shift in beam 2 [Eq. ...
As a potential means of measuring birefringence distribution, we analyzed the interference fringes based on three circularly polarized beams: a right-handed signal beam, a left-handed reference beam, and a right-handed reference beam. All beams were crossed at the same angle on the interfering plane, creating a two-dimensional interference fringe with three grating vectors. We proposed that by analyzing the interference fringes, we can measure the anisotropic phase shift in the signal beam. The obtained features of the anisotropic phase shift can be extended to the measurement of two-dimensional birefringence distributions without rotational manipulations of the objectives or polarizers. The fringes were generated by monolithic gratings, which can generate three-beam interfering fields precisely and easily. Finally, we confirmed the feasibility of a birefringence measurement system without any rotational manipulations of optics.
... An example of the hexagonal grating induced in a three-step illumination procedure in which the azomaterial film is rotated by 120° at each step is shown in Figure 10A-B, while a quasicrystal pattern [91,194] with 10-fold symmetry resulting from five subsequent irradiation steps (each for a rotation angle π/5) is shown in Figure 10C-F. Other complex and periodic superficial textures can be achieved also in experiments where irradiation is accomplished with three or more interfering beams [75,[195][196][197]. ...
The illumination of azobenzene molecules with UV/visible light efficiently converts the molecules between trans and cis isomerization states. Isomerization is accompanied by a large photo-induced molecular motion, which is able to significantly affect the physical and chemical properties of the materials in which they are incorporated. In some material systems, the nanoscopic structural movement of the isomerizing azobenzene molecules can be even propagated at macroscopic spatial scales. Reversible large-scale superficial photo-patterning and mechanical photo-actuation are efficiently achieved in azobenzene-containing glassy materials and liquid crystalline elastomers, respectively. This review covers several aspects related to the phenomenology and the applications of the light-driven macroscopic effects observed in these two classes of azomaterials, highlighting many of the possibilities they offer in different fields of science, like photonics, biology, surface engineering and robotics.
... We have also conducted studies on producing LC diffractive gratings with photocrosslinkable polymer LCs (PCLCs) [3][4][5][6][7]. ...
... Therefore, controlling this spatial distribution of the anisotropy is very important in achieving unique light control characteristics. To produce a two-dimensional anisotropic distribution, several approaches have been proposed so far [7][8][9]. ...
To fabricate two-dimensional anisotropic diffractive optical elements, the polarization drawing method using polarization-sensitive liquid-crystal polymers and a galvano scanner offers a flexible approach. This method produces an arbitrary anisotropic distribution in the polymer films by controlling the polarization state of an ultraviolet laser beam during scanning. The fabrication of two patterned anisotropic diffractive elements, which cannot be fabricated using conventional methods of polarization holography, demonstrates its efficacy. In addition, we also fabricate a liquid-crystal Fresnel lens using this method. Our approach has the potential to produce highly functionalized diffractive optical elements having complex anisotropic spatial distributions.
... Two-dimensional photonic crystals with optical anisotropy based on molecular alignment caused by the polarization modulation of interference fields were demonstrated using photo-crosslinkable liquid crystalline polymers. Ono and coworkers reported both optical properties and theoretical treatment [58,59]. The side-chain type LCP has a cinnamic moiety in its terminal region [60,61]. ...
Photocontrol of molecular alignment is an exceptionally-intelligent and useful strategy. It enables us to control optical coefficients, peripheral molecular alignments, surface relief structure, and actuation of substances by means of photoirradiation. Azobenzene-containing polymers and functionalized liquid crystalline polymers are well-known photocontrollable materials. In this paper, we introduce recent applications of these materials in the fields of mechanics, self-organized structuring, mass transport, optics, and photonics. The concepts in each application are explained based on the mechanisms of photocontrol. The interesting natures of the photocontrollable materials and the conceptual applications will stimulate novel ideas for future research and development in this field.
The ability of optical axis gratings (OAGs) to fully transfer the energy of an unpolarized incident light beam into the +/- 1st diffraction orders is explored below for development of a polarization-independent optical system with nonlinear transmission. Diffractive properties of OAGs based on azo dye doped liquid crystals (azo LCs) are efficiently controlled with low power radiation. Switching from diffractive to transmissive states of the OAG takes place within 50 ms at 60 W/cm(2) power density level, while the diffractive state is restored within similar to 1 s in the absence of radiation. High contrast optical switching is demonstrated with violet as well as green laser beams. A photoswitchable OAG is paired with a light-insensitive OAG in diffraction compensation configuration to obtain an optical system switchable from high to low transmission state. The thinness of OAGs required for high contrast switching ensures high overall transmission of the system. Given also the spectrally and angularly broadband nature of OAG diffraction and the capability of azo LC material systems to respond both to cw as well as short laser pulses makes the optical system under discussion very promising for optical switching applications. Presentation of these results is preceded by an "opinionated" review of prior developments and demystifying of the fabrication technique of high efficiency large area OAGs.
The ability of optical axis gratings (OAGs) to fully transfer the energy of an unpolarized incident light beam into the ±1st diffraction orders is explored below for development of a polarization-independent optical system with nonlinear transmission. Diffractive properties of OAGs based on azo dye doped liquid crystals (azo LCs) are efficiently controlled with low power radiation. Switching from diffractive to transmissive states of the OAG takes place within 50 ms at 60 W/cm2 power density level, while the diffractive state is restored within ~ 1 s in the absence of radiation. High contrast optical switching is demonstrated with violet as well as green laser beams. A photoswitchable OAG is paired with a light-insensitive OAG in diffraction compensation configuration to obtain an optical system switchable from high to low transmission state. The thinness of OAGs required for high contrast switching ensures high overall transmission of the system. Given also the spectrally and angularly broadband nature of OAG diffraction and the capability of azo LC material systems to respond both to cw as well as short laser pulses makes the optical system under discussion very promising for optical switching applications. Presentation of these results is preceded by an "opinionated" review of prior developments and demystifying of the fabrication technique of high efficiency large area OAGs.
We have developed holographic gratings that enable the asymmetric polarization conversion between ± 1-order diffraction beams. The holographic gratings are formed by polarization holography in a poly[(methyl methacrylate)-co-(disperse yellow 7 methacrylate)] film and show both anisotropic phase and surface modulations. For an azobenzene-containing polymer film, molecular reorientation and migration are strongly dependent on the polarization state of the writing beams and can be spatially modulated. Theoretical investigation by the Jones matrix method including both modulations has shown that the polarization ellipticity of ± 1-order diffraction changes as a function of relief depth. Experimental results in accordance with theoretical predictions show that the polarization gratings diffract linearly and circularly polarized beams simultaneously.
