Optically addressed modulator for tunable spatial polarization control.

We present an optically addressed non-pixelated spatial light modulator. The system is based on reversible photoalignment of a LC cell using a red light sensitive novel azobenzene photoalignment layer. It is an electrode-free device that manipulates the liquid crystal orientation and consequently the polarization via light without artifacts caused by electrodes.

Nanoplasmonically-engineered random lasing in organic semiconductor thin films.

We demonstrate plasmonically nano-engineered coherent random lasing and stimulated emission enhancement in a hybrid gain medium of organic semiconductors doped with core-shell plasmonic nanoparticles. The gain medium is composed of a 300 ± 2 nm thin waveguide of an organic semiconductor, doped with 53 nm gold nanoparticle cores, isolated within silica shells. Upon loading the nanoparticles, the threshold of amplified spontaneous emission is reduced from 1.

Cholesteric Polymer Scaffolds Filled with Azobenzene-Containing Nematic Mixture with Phototunable Optical Properties.

The past two decades witnessed tremendous progress in the field of creation of different types of responsive materials. Cholesteric polymer networks present a very promising class of smart materials due to the combination of the unique optical properties of cholesteric mesophase and high mechanical properties of polymer networks. In the present work we demonstrate the possibility of fast and reversible photocontrol of the optical properties of cholesteric polymer networks.

Stable selective gratings in LC polymer by photoinduced helix pitch modulation.

A cholesteric mixture based on the nematic liquid crystalline side-chain polymer doped with a chiral-photochromic compound was prepared and used as an active medium for creation of stable polarization selective gratings by phototunable modulation of the helix pitch. Such modulation was fabricated in the polymer mixture by a nonpolarized UV-irradiation with spatially modulated intensity that causes E-Z isomerization of a chiral-photochromic dopant, decreasing its helical twisting power. It was shown that the gratings recorded by UV-exposure through a mask are strongly selective to the handedness of circular polarized light.

Influence of Chromophore Length and Acceptor Groups on the Optical Properties of Rigidified Merocyanine Dyes.

Three series of rigidified tri-, penta- and heptamethine merocyanine dyes were synthesised. A piperidyl moiety was chosen as the electron-donating substituent while the electron-accepting group was varied from ketones to malononitriles and cyanoacetates. The structures of the compounds in the solid state and in solution were elucidated by X-ray diffraction and NMR spectroscopy, respectively, while optical properties were investigated by absorption and emission spectroscopy.

Influence of Chromophore Length and Acceptor Groups on the Optical Properties of Rigidified Merocyanine Dyes.

Invited for this month's cover are the three collaborating groups from the University of Stuttgart and the Fraunhofer Institute for Applied Polymer Research in Potsdam, both from Germany as well as the University of Windsor, Canada. The cover picture shows the shift of frontier orbital energies and symmetries upon excitation with light for three different chromophore lengths. Read the full text of the article at 10.

Formation of surface relief grating in polymers with pendant azobenzene chromophores as studied by AFM/UFM.

We studied peculiarities of the structural reconstruction within holographically recorded gratings on the surface of several different amorphous azobenzene-containing polymers. Under illumination with a light interference pattern, two processes take place in this type of polymer. The first process is the light-induced orientation of azobenzene units perpendicular to the polarization plane of the incident light.

New photorotor for the induction of anisotropy.

A new class of photosensitive compounds generates optical anisotropy comparable to azobenzene systems upon irradiation with linearly polarized light, but, in contrast to these systems, the new photorotor system does not absorb in the visible range. High values of dichroism and birefringence are induced and in the case of LC polymers the light induced order can be amplified by self-organization.

Single step optical fabrication of a DFB laser device in fluorescent azobenzene-containing materials.

Distributed feedback (DFB) lasers are produced directly in fluorescent azobenzene-containing materials using a single holographic optical step. Surface relief grating capable of producing images in fluorescence microscopy can be holographically formed in a number of materials.

Novel generation of liquid crystalline photo-actuators based on stretched porous polyethylene films.

The preparation of photo-actuators based on stretched porous polyethylene and an azobenzene-containing liquid crystalline polymer network is reported for the first time. It is revealed that this kind of photo-actuator possesses the following advantages: the lack of a need for using aligning coatings and cells preparation, high deformation of the actuator and its complete reversibility, good mechanical properties, and relatively low cost of fabrication. In addition some kinetic and thermodynamic features of the bending and unbending processes have been studied.

Efficient single-beam light manipulation of 3D microstructures in azobenzene-containing materials.

Large aspect ratio 3D microstructures (arrays of square posts and linear rectangular gratings) fabricated in a number of azobenzene-containing materials by soft lithography were manipulated by a single beam of polarized light. The materials exhibited different response to the beam orientation and the direction of light polarization. An elongation of the square posts both along and perpendicular to the polarization plane was observed depending on material.

Voltage-controlled compression for period tuning of optical surface relief gratings.

This Letter reports on new methods and a consistent model for voltage tunable optical transmission gratings. Elastomeric gratings were molded from holographically written surface relief gratings in an azobenzene sol-gel material. These were placed on top of a transparent electroactive elastomeric substrate.

Phenomenology of photoinduced processes in the ionic sol-gel-based azobenzene materials.

Very recently, supramolecular azobenzene-containing materials have been demonstrated to be effective for holographic inscription of surface relief gratings. High efficiency of grating formation in these materials is advantageously combined with easy material preparation because of the supramolecular principle of building blocs combination, availability of chemical components, and good film-forming properties. The materials show great promise for wide optical applications.

The fabrication of periodic polymer/silver nanoparticle structures: in situ reduction of silver nanoparticles from precursor spatially distributed in polymer using holographic exposure.

A new approach to producing volume periodic polymer-metal nanoparticle structures is presented. Periodic distribution of Ag nanoparticles in a polymer film can be obtained by applying the holographic patterning in the UV or visible spectral range to the composite material comprising photocurable monomers, photoinitiators and a solution of silver nitrate in acetonitrile. Photopolymerization of the composite in the interference pattern provides formation of a highly efficient volume grating composed of periodic polymer regions and Ag precursor-containing regions.

Three-dimensional planarized diffraction structures based on surface relief gratings in azobenzene materials.

The method of step-by-step formation of correlated 3D phase optical structures is presented. Surface relief gratings (SRG) recorded in azobenzene polymer layers are alternated with layers of a spacer polymer with a different refractive index. A pair of azobenzene and spacer polymers with excellent compatibility makes it possible to prepare layers of good optical quality in a stack without destruction of SRG in the previous layer.

Large-scale synthesis of organophilic zirconia nanoparticles and their application in organic-inorganic nanocomposites for efficient volume holography.

We present a multigram scale, one-step nonaqueous synthesis route to monodisperse, highly crystalline ZrO(2) nanoparticles. The nanoparticles can be stabilized in nonpolar solvents via a simple functionalization procedure using only minute amounts of organic stabilizers. Their great potential in materials applications is demonstrated by the fabrication of organic-inorganic nanocomposites that can be selectively photopolymerized to inscribe extremely effective and volume holographic gratings with the highest refractive index contrast (n(1) of up to 0.

Waveguide spectroscopic characterization of 3D anisotropies in conventionally photooriented and annealed films of liquid crystalline and amorphous azobenzene polymers.

Films of azobenzene-containing polymers were photooriented in the glassy state in such a way that the azobenzene side groups were oriented preferably perpendicular to the electric field vector. In the case of liquid crystalline polymers ,the photoinduced anisotropies generated in the glassy state were modified by thermotropic self-organization due to annealing above T(g). The conventional photoorientation process results in an oblate order.

Cholesteric polymer guest-host mixture with circularly polarized fluorescence: two ways for phototuning of polarization and its intensity.

A photosensitive fluorescent cholesteric guest-host mixture consisting of a nematic polyacrylate, a chiral, photochromic dopant sensitive to UV light, and a fluorescent dopant was prepared. The nematic polyacrylate contains 4-phenyl-4'-methoxybenzoate nematogenic side groups and photochromic 4-cyanoazobenzene side groups. The chiral-photochromic dopant formed by isosorbide and cinnamic acid is capable of E-Z photoisomerization and [2 + 2] photo-cycloaddition under light irradiation.

Thermally stable holographic surface relief gratings and switchable optical anisotropy in films of an azobenzene-containing polyelectrolyte.

In a search for effective polymer film material for holographic surface patterning, commercially available azobenzene polyelectrolyte has been employed. Films of good optical quality in a wide range of thickness were produced. Optical dichroism up to 0.

Perylenediimide-surfactant complexes: thermotropic liquid-crystalline materials via ionic self-assembly.

In this communication we present the facile preparation and characterisation of thermotropic liquid-crystalline materials from the ionic self-assembly of a charged perylenediimide derivative and oppositely charged surfactants.