Poling and relaxation dynamics of side-chain and crosslinkable polymers

The growth of the macroscopic second order nonlinear optical properties of side-chain and crosslinkable copolymer species is theoretically modelled. The model describes the rotational diffusion of nonlinear diazo-dye dipoles, in the presence of crosslinking sites randomly distributed in the copolymer matrix, under application of a periodic electric poling field. The time dependence of the orientational probability distribution for the crosslinked dipoles has been calculated. Such distribution have been used in order to evaluate the temporal growth of the second order nonlinear optical properties and their asymptotic value when saturation of the crosslinking process is attained. The results of the theoretical model are compared to the experimental ones, obtained for a crosslinkable copolymer, Red Acid Magly. In the experiments the r33 component of the electro-optic coefficient is measured by means of a modified electro-optic ellipsometry setup. The comparison shows a good agreement between experimental and numerical results. The model can be used in order to find the best values of the copolymer parameters, necessary in order to maximize the final second order nonlinear optical properties

Pulse poling of side chain and crosslinkable polymers

The growth of the macroscopic second-order nonlinear optical properties of side-chain and crosslinkable copolymer species is theoretically modeled. The model describes the rotational diffusion of nonlinear diazo-dye dipoles, in the presence of crosslinking sites randomly distributed in the copolymer matrix, under application of a periodic electric poling field. Solutions for the fundamental equations, describing the time-dependent orientational probability distribution for the crosslinked dipoles, have been obtained in the frame of two complementary approximations. Such distributions have been used in order to evaluate the temporal growth of the second-order nonlinear optical properties and their asymptotic value when saturation of the crosslinking process is attained. The two approximations are shown to give equivalent results, in the range of parameters where both are valid. The influence of the poling electric field frequency and of the volume density of crosslinking sites on the asymptotic second-order nonlinear optical properties is discussed. The results of the theoretical model are compared to the experimental ones, obtained for two copolymers species: A Disperse red 1 side-chain copolymer and a crosslinkable evolution of the latter, Red acid magly. In the experiments the r33 component of the electro-optic coefficient is measured by means of a modified electro-optic ellipsometry setup. The comparison shows a good agreement between experimental and numerical results. The model can be used in order to find the best values of the copolymer parameters, necessary in order to maximize the final second-order nonlinear optical properties

Temperature- and light-induced relaxation of the electro-optic properties of poled side-chain copolymers

We report on the measurement of the time relaxation of the electro-optic properties of poled side-chin copolymers under illumination with absorbed laser radiation. Films of side- chain Disperse Red 1 substituted poly-Methyl-Methacrylate were sandwiched between ITO and gold electrodes and poled with a standard temperature/electric field cycle. The decay of the electro-optic properties, measured by means of the Teng and Man ellipsometric reflection technique at (lambda) equals 830nm, was measured for several intensities of a circular polarized absorbed laser beam, (lambda) equals 514.5nm, illuminating the sample. The relaxation shows a stretched exponential time dependence, with intensity dependent decay and stretching constants. The relaxation curves are compared with those obtained, for the same sample, in standard temperature stimulated non linear dielectric relaxation measurements

Study of the orientational relaxation dynamics in a nonlinear optical copolymer by means of a pole and probe technique

We report measurements on the isothermal relaxation dynamics of the electro‐optic coefficient of electric field poled polymeric films. The studied copolymer is a side‐chain Disperse Red 1/poly–methyl–metacrylate combination. The isothermal relaxation is shown to follow a Kohlrausch–Williams–Watts stretched exponential dependence, whose parameters are strongly dependent on temperature. The average decay constant is shown to follow an Arrhenius temperature dependence below the glass transition Tg, while it is described by a Vogel–Fulcher–Tamann–Hesse above Tg. The values of the decay constant confirm a much better stability of the polymer orientation with respect to guest‐host systems. The relaxation is shown to be due to a broad distribution of relaxation rates, the width of which can be qualitatively described by an empirical relation, which has already been used for guest‐host systems. The measurement technique permits monitoring relaxation in a standard dielectric relaxation configuration and performing unconventional poling of the samples

Real-time pole and probe assessment of orientational processes in electro-optic polymers

The electro‐optic properties of polymer films are measured by an original technique whereby a periodic sequence of poling and probing steps permits alternation of the application of orientation and dephasing potentials. Relaxation dynamics of the electro‐optic coefficient of Red–Acid–Magly crosslinkable polymer films is studied as a function of the temperature of the samples. The time constant of the decay τ as measured at several temperatures is found to follow a Vogel–Fulcher–Tamann—Hesse dependence, for temperatures above glass transition. Poling the samples in the presence of a pulsed electric field leads to a r33 electro‐optic coefficient as high as 6 pm/V

Synthesis and Characterization of Aromatic Polyimides Bearing Nonlinear Optical Chromophores

International audienceThe syntheses and characterizations of two aromatic polyimides with nonlinear optical (NLO) chromophore side chains were investigated through a two-step synthetic route. These two polymers were prepared by polycondensation of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) with 4-(4-amino, 2-hydroxy) phenoxyaniline (HODA) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), respectively. First the poly(hydroxy)imides were prepared by direct thermal imidization. The resulting polyimides bearing hydroxy groups were found to react easily with the terminal hydroxy group of the chromophore (Disperse Red1 (DR1)) via the Mitsunobu reaction. The high content of chromophore for the polyimide with 6FAP diamine was confirmed by UV spectroscopy and ellipsometry spectroscopy measures. The resulting NLO polyimides possess high glass transition temperatures (Tg > 185°C), excellent solubilities and processabilities even though the extent of chromophore grafting is up to 95 mol%. The second harmonic coefficient (d 33) at the wavelength of 1320 nm is close to 30 pm V−1. The thermal and temporal stabilities of the NLO properties were investigated. The relaxation temperature of the SHG signal measured at the 50% decay of the initial SHG signal (I 2ω/2 at 2°C min−1) was 168°C for the polyimide based on HODA and 157°C for the polyimide based on 6FA

Synthesis and characterization of fluorinated crosslinkable oligoimides with linear and nonlinear optical properties

International audienc

Synthesis and characterization of fluorinated crosslinkable oligoimides with linear and nonlinear optical properties

International audienc