Effect of 2-Methylthiazole Group on Photoinduced Birefringence of Thiazole-Azo Dye Host-Guest Systems at Different Wavelengths of Irradiation.

The photoinduced birefringence behaviors of host-guest systems based on heterocyclic thiazole-azo dyes with different substituents, dispersed into PMMA matrix, were investigated under three excitation wavelengths, i.e., 405 nm, 445 nm or 532 nm. The wavelengths fell on the blue side, near the maximum or on the red side of the absorption bands of trans-azo dyes, respectively. We found that photoinduced birefringence was generated at a similar extent in all studied systems, except the system containing a 2-methyl-5-benzothiazolyl as thiazole-azo dye substituent. For this material, the achieved birefringence value was the highest among the whole series, regardless of the excitation wavelength. Moreover, we identified the optimal irradiation wavelength for efficient birefringence generation and showed that large absorption of excitation light by trans isomer does not account for achieving a significant degree of molecular alignment. The obtained results indicate that thiazole-azo dye with a 2-methyl-5-benzothiazolyl substituent shows promising photoinduced birefringence, and can be considered a dye potentially suitable for optical applications.

Fully updatable three-dimensional holographic stereogram display device based on organic monolithic compound.

Holographic technique is a unique method to reproduce object on a device in three dimensions (3D). It allows us real 3D images with full parallax without special eye glasses or any special optical devices. we present fully updatable holographic 3D display system using a holographic stereographic technique with a transparent optical device of poly(methylmethacrylate) doped organic compound of 3-[(4-nitrophenyl)azo]-9H-carbazole-9-ethanol (NACzE). 100 elemental holograms which are a series of pictures of object took from different angles can completely reproduce updatable entire hologram of object. Former hologram of object can be over-recorded and immediately replaced by new hologram of object without erasing process. Typical recording time for an elemental hologram is 200 ms, and total recording time including translational stage movement for 100 elemental holograms is 28 s. The present system with preferred memory is a good candidate for 3D signage application.

Photoinduced grating formation in a polymer containing azo-carbazole dyes.

Although some azo-carbazole derivatives attached on or doped into inert polymers are known to show photorefractive effect without external electric field, the origin of their asymmetric energy transfer in two-beam coupling experiments were unknown. We made the two-beam coupling experiment followed by sample translation and one-beam diffraction at 633 nm for thick films composed of 3-[(4-nitrophenyl)]azo-9H-carbazole-9-ethanol (NACzEtOH) and poly(methylmethacrylate), finding that photoinduced gratings grew in several minutes accompanied with phase displacement of the gratings, but the phase shift was not always synchronized with the refractive index modulation. We reformulated the Kogelnik's coupled-wave theory with strict energy conservation law for analysis. Comparison of the grating growth and erasure at 532 nm to Disperse Red 1 (DR1), the most well-known azo dye showed that the photoisomerization was dominant at this wavelength and that the azo-carbazole dyes were faster in response time and more resistive to erasure than DR1.

Generation of a broadband spectral comb with multiwave mixing by exchange of an impulsively stimulated phonon.

A broadband spectral comb is generated around the third harmonics of incident light with the nondegenerate, impulsively stimulated Raman scattering technique using ultrashort light pulses. The comb has a spectral width of more than 4000 cm(-1), and its envelope becomes smooth as the light powers are increased. It consists of discrete lines, the spacing of which is equal to the frequency of the Raman-active phonon mode, even though the frequency of the phonon mode is far smaller than the frequency difference between the two incident light pulses. The multiline structure is generated with multiwave mixing by exchange of the impulsively stimulated phonon among the signals.