Hiro Matsuda

Large near-resonance third-order nonlinearity in an azobenzene-functionalized polymer film

The third-order nonlinear optical response of a thin film containing the azobenzene dye Disperse Red 1 was studied using the z-scan technique with tunable picosecond pulses. A nonlinear refractive index of −5.0 cm2/GW, corresponding to a Re χ(3)=−3.0×10−15 m2/V2 (2.1×10−7 esu), has been measured at 570 nm. The observed nonlinearity is attributed to the change in refractive index induced by the trans-cis transition in the dye molecule.

Photoinduced surface relief gratings on azopolymer films: Analysis by a fluid mechanics model

Photoinduced surface relief grating (SRG) formation on azopolymer films is discussed precisely using a fluid mechanics model which takes depth dependence of photoinduced driving force and velocity distribution in the film surface into account. Formulation for the SRG dynamics is derived analytically as a function of film thickness and interference wave number. The film thickness dependence of diffraction efficiency, which is observed experimentally, agrees well with the theoretical value in the entire range of film thickness. The dependence of SRG driving force on interference wave number is also discussed in terms of the experimental data using proposed model.

Molecular design on substituted DAST derivatives for second-order nonlinear optics

Abstract Molecular design of the derivatives of 1-methyl-4-(2-(4-(dimethylamino)phenyl)ethynyl)pyridinium (DAS) was investigated from the following two points, i.e., simple substitution of one aromatic hydrogen atom to enhance hyperpolarizability β and fluorine substitution to decrease optical loss due to overtones of C–H bond vibration. By the screening using semiempirical calculation, 2-cyano-1-methyl-4-(2-(4-(dimethylamino)phenyl)ethynyl)pyridinium 7, 2,3,5,6-tetrafluoro-1-methyl-4-(2-(4-(dimethylamino)-2,3,5,6-tetrafluorophenyl)ethynyl)pyridinium 10, etc. were expected to have larger β than that of DAS. The salts of 7 and 1-methyl-4-(2-(4-(dimethylamino)-2,3,5,6-tetrafluorophenyl)ethynyl)pyridinium as a related cation of 10 were synthesized and four crystals showing second-harmonic generation were found.

Photomodification of polymer films: azobenzene-containing polyurethanes

New results are presented on optical recording to the films of polymers substituted with azo dyes. Holographic gratings are formed in the polyurethane films by exposure to laser light without any post-treatment as in previous works using polyacrylates, epoxy-based polymers and polyesters substituted with azo dyes. It is shown for the first time that the principal mechanism of optical recording could be the mass transfer of polymers during the cis-trans isomerization of azo dye units on the polymers from illuminated areas to non-illuminated areas. Besides this transport, some irreversible photochemical reactions involving atmospheric oxygen are suggested as another possible origin for the holographic recording.

Photoinduced surface relief formation on azopolymer films: A driving force and formed relief profile

A driving force of photoinduced surface relief (PSR) formation is examined by considering the complex electric susceptibility of the absorbing medium. It is introduced into a fluid mechanics model established for the viscous fluid layer on a flat substrate. As a result, a theoretical model for PSR formation covering thoroughly from the origin of the driving force to the dynamic process forming the surface relief is established. A series of systematic experiments are carried out by means of one-dimensional sinusoidal and Gaussian beam irradiation and the results are reproduced well by the model calculation. The experimental results reported in former literature are also reviewed using this model and the result supports strongly our assumption: driving force derived from the interaction between the absorbing medium and optical electric field acts as a body force on the optically plasticized azopolymer. Further, from the consideration based on the model, some important features of PSR formation which have no...

Photoreversible optical nonlinearities of polymeric films containing spiropyran with long alkyl chains

It was demonstrated that the third‐order optical nonlinearity of polymer films could be reversibly controlled by the photochromic conversion and following J‐aggregate formation of spiropyran embedded in an inert polymer matrix. Patterns consisting of areas with high and low third‐order nonlinear optical activities were prepared by imagewise exposure of the photochromic films followed by thermal treatment to form thermally stable J aggregates of photoinduced merocyanine in the exposed area. This system could be useful in developing new unconventional optical devices based on optical nonlinearities, including new types of spatial light modulators.

Unconventional polarization characteristic of rapid photoinduced material motion in liquid crystalline azobenzene polymer films

We carried out double-beam interference experiments using an argon ion laser with controlled polarization in order to cause the formation of photoinduced surface relief in liquid crystalline azobenzene polymer films. The irradiation was undertaken on a film in the cis-rich state obtained by a pre-exposure to ultraviolet light. In this procedure, the efficiency of the photoinduced mass transfer was high, more than 1000 times greater than hitherto reported for amorphous azobenzene polymers. This approach revealed the unusual nature of the migration process. Rapid mass migration is promoted by intensity holographic recording, independent of the polarization of the light used for the irradiation. This insensitivity with respect to the polarization of the light led us to the conclusion that rapid mass migration starting from a cis-rich azobenzene polymer is predominately driven by phototriggered elemental processes such as local dewetting, self-organizing motion, and translation diffusion.

Ethyl-Substituted Stilbazolium Derivatives for Second-Order Nonlinear Optics

1-Methyl-4-(2-(4-(dimethylamino)phenyl)ethenyl)pyridinium iodide and its three analogues with ethyl-substituted cations were prepared. The solubility in organic solvents was confirmed to increase by ethyl substitution. Counter anion exchange afforded several SHG active crystals even in ethyl-substituted derivatives, and 1-ethyl-4-(2-(4-(dimethylamino)phenyl)ethenyl)pyridinium p-nitrobenzenesulfonate was estimated to have an off-diagonal d component twice as larger as that of 1-methyl-4-(2-(4-(dimethylamino)phenyl)ethenyl)pyridinium p-toluenesulfonate (DAST).

Competitive effects of grooves and photoalignment on nematic liquid-crystal alignment using azobenzene polymer

Effect of an anisotropic photoalignment layer and microgrooves on nematic liquid-crystal (LC) alignment was quantitatively examined using azobenzene polymer thin film with surface relief grating (SRG) of about 1 μm pitch. The SRG with various modulation depths was treated with polarized light irradiation to align molecules at 45° from the groove. Nematic LC molecules, 4′-n-pentyl-4-cyanobiphenyl, orient to the photoaligned direction on the SRG being shallower than 200 nm. The orientation rather sharply deviates from the photoaligned direction toward the groove direction with increasing grating depth into the deeper region than 200 nm and finally becomes parallel to the grooves on the SRG of 400 nm deep. This behavior is successfully simulated by the consideration of anisotropic surface interaction and an elastic energy of LCs.

Evaluation of |β| of stilbazolium p-toluenesulfonates by the hyper Rayleigh scattering method

The hyper Rayleigh scattering (HRS) method was applied to determine the absolute value of second-order hyperpolarizabilities ((beta) ) of stilbazolium p-toluenesulfonates and related ionic species in methanol. In general, the (beta) values of stilbazolium derivatives become large with increasing wavelength of absorption maximum and are 1.1 X 10-28 - 3.9 X 10-28 esu, i.e., 3 - 10 times larger than (beta) of p-nitroaniline. By way of exception, halogenated stilbazoliums showed rather larger (beta) compared with the unsubstituted stilbazolium having almost the same absorption cutoff and maximum. The calculated d value of hydroxystilbazolium p-toluenesulfonate obtained using the present (beta) and the known crystal structure agreed well with the experimental d value by the Maker fringe method.