No abstract

Microlenses and microlens arrays with a diameter smaller than several millimeters are key elements in optical devices with growing miniaturization. [1][2][3] Planar microlens arrays of the gradient-index (GRIN) type are useful: other optical components can be connected directly to the surface of the lenses, because the focusing effect originates from the internal refractive-index distribution. Ion exchange in glass is currently the most common technique for the production of such GRIN microlens arrays, [4] along with electromigration, diffusion polymerization, [5] and laser-beam writing.[6] Although these methods give high-quality microelements, their fabrication requires expensive equipment, multiple sophisticated processes, and long timescales, and, additionally, they involve health hazards. Here we show a much simpler fabrication method for microlens arrays that combines photoinduced reorientation of dye-doped liquid-crystal-liquid-crystal (LC-LC) monomer mixtures and simultaneous photopolymerization. A microlens array was obtained upon successive irradiation of the desired arrangement, at the positions of the individual lenses, with a 488 nm beam . Each microlens in the array exhibited polarization selectivity with respect to incident polarized actinic light, and was arranged in a desired polarization direction. We achieved fabrication of microlens arrays with desired patterns and polarization selectivity in this simple manner. These results imply that microlens arrays fabricated by using this technique could have potential applications as key components in optical parallel-processing systems and large-scale free-space networks. Precise regulation of a spatial distribution of refractive index in an area as small as < 1 mm is especially important for fabricating GRIN microlens arrays. As LCs have a large birefringence, which can be controlled by an external field, various optical components that use LC materials have been applied to practical applications. [7][8][9] LC microlens arrays are a new type of planar microlens array, which are composed of LC materials and driven by an electric field that leads the LC materials to exhibit a lenslike refractive-index distribution.[10] We have previously reported that the oligothiophene TD (5,5″-bis(5-butoxycarbonyl-2-thienylethynyl)-2,2′:5′,2″-terthiophene) (Figure 1a) acts as a highly efficient dye for photoinduced reorientation of LCs, [11,12] which is attributed to the polarized excitation of dye molecules and the resultant large change in guesthost interaction. [13,14] Upon exposure to a laser beam above a threshold intensity, anisotropic director reorientation of LCs produces a spatially inhomogeneous distribution of the refractive index. The reoriented LC sample can be used, therefore, as a phototunable microlens whose index profile can be varied by the light intensity.To obtain a stabilized LC microlens, a certain amount of an LC monomer was added to some LCs. It is well known that photopolymerization of LC monomers stabilizes the alignment of LCs, and after thi...

The photoinduced reorientation behavior of dye-doped nematic liquid crystals (LCs) was investigated. Thiophene derivatives with ester moieties were newly synthesized as the guest dye molecule. The liquidcrystalline behavior and optical properties of these compounds were evaluated, and the effect of the dye structure on the photoinduced reorientation behavior of the dye-doped LCs was investigated. The photoinduced formation of diffraction rings was observed as a result of the self-phase modulation effect at the intensity of 11 W/cm 2 , when an Ar + laser beam at 488 nm was irradiated above the threshold intensity. Comparison of the lowest threshold light intensity for the appearance of the diffraction rings revealed that the thiophene dye with ester moieties directly bound to the terminal thiophene shows a lower threshold intensity than those of any other dyes.

Neutron diffraction measurements have been carried out on aqueous 4 mol% glycine solutions. The H/D isotopic substitution technique was applied to both methylene-hydrogen (HM) and water-hydrogen (HW) atoms in order to obtain information concerning the hydration structure around the methylene group within the glycine molecule. Structural parameters for the first hydration shell of the methylene-hydrogen atoms were determined as r(HM···OW) = 2.64(1) Å and r(HM···HW) = 2.87(1) Å from the least squares fitting analysis of the observed first-order difference function, 0HΔH(Q), and the partial structure factor, aHMHex(Q), respectively. The first hydration shell of the methylene group involves ca. 2 water molecules per one glycine molecule.

Time-of-Flight (TOF) and steady state reactor neutron diffraction measurements have been carried out for aqueous 2.5 mol% Dl- and l-alanine solutions in order to investigate the differences in intermolecular hydrogen-bonded structure between solutions involving amino acid molecules with different optical activities. The observed difference functions, Δi(Q) and Δiinter(Q), between observed scattering cross sections for Dl- and l-alanine solutions with a D content of 96.1% exhibit the first peak located at Q = 2 Å−1 followed by oscillatory features extending up to the higher-Q region. The difference distribution function, Δg(r), obtained from the Fourier transform of Δi(Q), clearly indicates negative peaks at r = 2 and 2.5 Å and a positive one at r = 3.5 Å. Partial structure factors, aHH(Q), aXH(Q), and aXX(Q) (X: O, N, C, HM, and HM′, where HM and HM′ denote methyl and methine hydrogen atoms within the alanine molecule, respectively) for 2.5 mol% Dl-alanine solutions are successfully determined from combined analyses of intermolecular interference terms observed for solutions with 96.1, 66.0, and 35.9% exchangeable deuterium content. The nearest neighbor O···Hex and Hex···Hex (Hex: exchangeable hydrogen atom) distances are determined from the least squares fit of the observed partial structure factors, 1.90(1) and 2.48(1) Å, respectively. These values correspond to the positions of negative peaks observed in the present Δg(r) function. The least squares fitting analysis of the observed Δi(Q) revealed that the difference in the coordination number of the nearest neighbor O···Hex and Hex···Hex interactions between the Dl- and l-alanine solutions are −0.031(5) and −0.072(5), respectively. It is concluded that the intermolecular hydrogen bonds among solvent water molecules in the Dl-alanine solution are ca. 2% weaker than those in the l-alanine solution.