G. Seniutinas

Orientational relaxation of three different dendrimers in polycarbonate matrix investigated by optical poling

We report on all-optical poling relaxation of E-O active dendrimers photo-patterned in the polycarbonate matrix. Three kinds of polyester type dendrimers G0, G1 and G2 containing azobenzene in the core were used as second-order nonlinear optical active chromophores to create noncentrosymmetry inside the material. We used a guest–host type system of these structures spin-coated on a glass substrate. These samples were poled by using an all-optical poling method, where the polar electric field of electromagnetic waves enables us to orient dendrimer molecules creating a quasi-phase-matched grating of nonlinear second-order susceptibility χ(2). Molecular orientation and subsequent dark relaxation kinetics in the samples with different poling beam applied energies were measured. Theoretical modeling of the poling relaxation kinetic revealed a set of characteristic time constants, which were interpreted by different relaxation mechanisms.

Freezing out all-optical poling dynamics of azophenylcarbazole molecules in polycarbonate.

In this work we have extended the application of a theoretical model describing the processes of all-optical poling of isomerizable molecules while taking into consideration the thermoisomerization related findings presented in the literature. A model describing all-optical poling transients using a three relaxation rate approach was contrasted with the experimental results of azophenylcarbazole doped polycarbonate measured in a wide range of temperatures from 150 to 300 K, thus covering the β transition for the host. By means of a long timescale and low temperature, we were able to better resolve the thermoisomerization and orientational diffusion processes. The cis→trans thermoisomerization relaxation rates k1 and k2 were obtained in the range 10(-5) to 10(-2) s(-1) and the relaxation rate k3 of the orientational diffusion of the trans isomer in the range 10(-6) to 10(-4) s(-1). The rates exhibited diverse temperature dependent behaviors: the two lowest (k2,k3) manifested Arrhenius type dependencies (Ek2 = 157 meV), whereas, the highest (k1) showed a temperature dependence that is non-Arrhenius, or undistinguished for our experimental conditions. The latter was interpreted using the geometrical adjustment model. By investigating chromophore-polymer systems at temperatures far below Tg, we were able to uncover the situation when the cis→trans transition is switched-off and the orientational randomization is suppressed. Thus, we could consider the chromophores as frozen.

Photoinduced Optical Functionalism of Branched Azophenylcarbazoles in Molecular Glass Matrices

A new guest-host composition of 3-(4-nitrophenyl)azo-9-(2-ethyl)hexyl-2-(2-ethyl) hexyloxycarbazole as chromophore and 2,2-bis{4-[2-hydroxy-9-(carbazol-9-yl)-5-(carbazol-9-methyl)-4,7-dioxanonyloxy]phenyl}propane (molecular glass) as host for all-optical poling application was developed and investigated. A comparison between molecular glass and commonly used bisphenol Z polycarbonate as host showed a slightly better ability for the molecular glass to keep the azophenylcarbazole molecules oriented. Erasure while reading the non-centrosymmetry created is demonstrated and explained. Using an adopted model orientational diffusion coefficient, lifetime of cis isomer and probabilities of redistribution were evaluated.

Photo-Switching dynamics of azo-phenylcarbazoles in polycarbonate around β transition temperature

Second order non-linear optical features of azophenylcarbazole based derivative 9-(2,3-epoxy)propyl-2-(2,3-epoxy)propoxy-3-(4-nitrophenyl)azo-9H-carbazole in polycarbonate investigated at temperature 240 K, which is close to β transition for polycarbonate, are presented. Using all-optical poling technique writing and reading kinetics of second order susceptibility gratings in the azophenylcarbazole derivative were measured. Theoretical modelling of the experimental results indicates two cis-trans thermoisomerization rates in the range of k₁ = (2.5-3.3)×10^-3 s^-1, k₂ = (6.3-7.14)×10^-4 s^-1 depending on writing laser beam intensities (I_ω= 0.75-1.43 J/cm², I_2ω= 0.5-0.96 mJ/cm²); with slightly lower rates for the lower writing beam fluence. The orientational diffusion rate 1.43·10^-5 s^-1 does not depend on the writing conditions. The result indicates that the range of writing conditions used has very minor or even no influence over the intermolecular interaction observed during the all-optical poling process.

Optical poling of azo-compounds for applications in nanophotonics

Azo-compounds in polymers will likely play an increasingly important role in engineering of silicon photonics and plasmonic nano-devices for E-O modulation, parametric generation, switching and sensing. In this paper, we present a phenomenological theory of all-optical poling and photo-assisted electric field poling of azo-dye doped polymers and compare theoretical simulation results with experimental all-optical poling transients at varying temperatures obtained for azophenylcarbazole type azo-dyes in polycarbonate polymer matrix.

Azochromophore isomerization dynamics: From monomers to polymers

The synthesis and second order optical features of azophenylcarbazole based monomer 9-(2,3-epoxy)propyl-2-(2,3-epoxy)propoxy-3-(4-nitrophenyl)azo-9H-carbazol and polymeric azo dye AZAP are described. Relative higher optical poling efficiency was measured for the polymer, however, better stability, i.e. less orientational diffusion and thermal relaxation ability, were observed for the monomer. Modeling revealed parameters describing probability for molecules to rotate, orientational diffusion and thermal relaxation.

Picosecond reading of optically poled azophenylcarbazole

We report on reading process of poled media determined by duration and fluence of reading light. The poled media - oriented azophenylcarbazole molecules - was obtained by all-optical poling using nanosecond YAG laser radiation. While comparing picosecond and nanosecond pulses used for reading, it turned out that the power of light is dominating, if considering the erasure decay of poled media.

Third harmonic generation via dendrimers of four generations

We report on third harmonic generation of E-O active dendrimers dispersed in polycarbonate matrix. Four kinds of polyester type dendrimers G0, G1, G2 and G3 containing azobenzene in the core used as third order nonlinear optical active chromophores were prepared as guest-host type system based on polycarbonate matrix spin-coated on a glass substrate. Third harmonic generation was measured while exciting the samples with fundamental wavelength 1.064 ¿m. Non-linear third-order susceptibility ¿(3) for different generations of dendrimers was evaluated.