T. V. Krivenko

Photorefractive polymer composites for the ir region based on carbon nanotubes

The photorefractive properties of polymer composites based on aromatic polyimide and single-wall carbon nanotubes are studied using radiation at a wavelength of 1064 nm. It is found that the nanotubes possess photoelectric sensitivity in this spectral region and that the kinetic photorefractive characteristics of the polymer composites are entirely determined by the photogeneration and charge transport characteristics of the layers. The two-beam gain coefficient of the signal beam measured for a composite consisting of aromatic polyimide and 0.25 wt % of single-wall carbon nanotubes in a constant electric field E0 = 79 V/μm is equal to 84 cm−1 and exceeds the optical absorption coefficient by 59 cm−1. The refractive index modulation is equal to Δn = 0.004 at E0 = 54 V/μm.

Photoelectric, nonlinear optical and photorefractive properties of polyimide doped with J-aggregates of cyanine dye

Abstract Novel solid-state photorefractive compositions consisting of the aromatic polyimide ( T g is about 230 °C) and the thiacarbocyanine dyes were prepared. These systems have the high net gain coefficient, Γ − α , about 360 cm −1 . The dyes form the nanocrystalline J -aggregates that are responsible for photoelectric sensibility in the region of action of Ar–Kr laser and are known to have also very high third-order macroscopic polarizability. The Kerr electrooptical effect is mainly responsible for the light induced refractive index change. It is established that the charge photogeneration time constant determines the time of the photorefractive grating formation and depending on the dye used may be about 20 ms. So, it became possible to develop the solid-state high-performance photorefractive layers based on the polymer with high T g .

INFRARED PHOTOREFRACTIVE COMPOSITES BASED ON POLYIMIDE AND J-AGGREGATES OF CYANINE DYE

Photorefractive composites sensitive to 1064 nm on a base of an aromatic polyimide containing J-aggregates of a thiacarbocyanine dye are presented. The molecules of the dye form the nanocrystalline J-aggregates that are responsible for photoelectric sensitivity at 1064 nm and nonlinear third-order optical properties. The net gain coefficient 266 cm-1 and the response time 0.09 s were achieved at an external electric field of about 15 V/μm.

Photoelectric, nonlinear optical, and photorefractive properties of polyvinylcarbazole composites with graphene

Polyvinylcarbazole (PVK) composites containing graphene in an amount of somewhat less than 0.15 wt % exhibit third-order dielectric susceptibility due to the presence of graphene, as well as photoelectric and photorefractive sensitivity at 1064 nm. The photorefractive (PR) effect is known to occur in a polymer composite that possesses both photoelectric sensitivity and nonlinear optical properties. The photoelectric, nonlinear optical, and PR properties of PVK composites with graphene have been considered in this paper.

Infrared photorefractive composites based on polyvinylcarbazole and carbon nanotubes

Photorefractive materials based on unplasticized polymers that have a high glass-transition temperature and the frozen random orientation of chromophores were prepared by layer casting. Under these conditions, only the third-order susceptibility has a nonzero value, increasing with an increase in the conjugation-chain length and reaching considerable values in the case of nanosized molecules, such as single-wall carbon nanotubes (SWNTs). In SWNT-containing polyvinylcarbazole, the photoelectric sensitivity and photorefractive characteristics were measured at 1064 nm. Using electric-field induced second-harmonic generation, the third-order susceptibility was estimated. In a composite containing 0.26 wt % SWNT, the diffraction grating is displaced by 5° relative to the interference pattern, the result that is presumably due to the close mobility of unlike charge carriers. Therefore, the beam-coupling gain coefficient Γ and the net gain Γ-α have low values, which are 53 and 42 cm−1, respectively, at 115 V/μm.

Photoelectric, nonlinear optical, and photorefractive properties of composites based on poly(N-vinylcarbazole) and gallium phthalocyaninate

Poly(N-vinylcarbazole) layers containing tetra-5-crown-5-gallium phthalocyaninate (R4Pc)Ga(OH) are shown to possess photoelectric and photorefractive sensitivity at a wavelength of 1064 nm. This effect is associated with the formation of supramolecular ensembles of (R4Pc)Ga(OH) molecules with electronic optical absorption in the near-IR range and nonlinear optical properties. For the composite containing 5 wt % (R4Pc)Ga(OH) supramolecular ensembles, the dependence of the quantum efficiency of mobile-charge photogeneration on electric field E0 is well fit by the Onsager equation expanded to E03 at a quantum yield of electron-hole pairs of φ0 = 0.9 s with an initial separation radius of r0 = 9.8 A susceptibility χ(3) equal to 1.85 × 10−10 esu is measured via the well-known method of electric-field-induced second-harmonic generation. Two-beam-coupling gain coefficient Γ is found to be 80 cm−1 at E0 = 120 V/μm.

Photorefractive Polyimide Containing J-Aggregates of Thiacarbocyanine Dye

The paper demonstrates photorefractive characteristics of the aromatic polyimide (T_g=230\,^\circ\hbox{C}) containing J-aggregates of the thiacarbocyanine dye. The two wavelengths 647\,\hbox{nm} and 514\,\hbox{nm} of Ar-Kr-laser were used. The J-aggregates of the dye are responsible for optical absorption at 647\,\hbox{nm} . At that wavelength the net gain coefficient increases from \Gamma-\alpha=217\,\hbox{cm}^{-1} to 361\,\hbox{cm}^{-1} with growth of external electric field E_0 from 16 to 123\,\hbox{V}/\rmu\hbox{m} . Only samples containing J-aggregates exhibit the PR effect at wavelength 514\,\hbox{nm} at which the laser excites monomeric form of the dye. The estimated at 514\,\hbox{nm} and E_0=16\,\hbox{V}/\rmu\hbox{m} two-beam gain coefficient is near 480\,\hbox{cm}^{-1} and the net gain \Gamma-\alpha is about 118\,\hbox{cm}^{-1} . The high glass temperature of aromatic polyimide should appreciably limit the orientation...

Nonlinear Optical Properties of Systems Based on Ruthenium(II) Tetra-15-crown-5-phthalocyaninate

The third-order nonlinear optical properties of the ruthenium (II) complex with tetra-15-crown-5-phthalocyanine and axially coordinated triethylenediamine molecules (R4Pc)Ru(TED)2 were analyzed by means of the z-scanning technique. A solution of (R4Pc)Ru(TED)2 in tetrachloroethane was exposed to nanosecond laser pulses at a wavelength of 1064 nm. It was found that the third-order molecular polarizability of the Ru(II) complex is 4.5 × 10−32 cm4/C (esu). The polarizability per molecule increases by a factor of 3.6 when the single molecule occurs in a supramolecular assembly of (R4Pc)Ru(TED)2 complexes. The photoelectric and photorefractive properties at 1064 nm of polymer composites, determined by the supramolecular assemblies that exhibits optical absorption and photoelectric sensitivity in the near IR region, are reported.

Photorefractive IR-range composites on the basis of poly(vinyl carbazole) and ruthenium (II) tetra-15-crown-5-phthalocyanines

The photoelectric sensitivity and photorefractive properties at 1064 nm of composites consisting of poly(vinyl carbazole) (PVC), complexes of ruthenium(II) with tetra-15-crown-5-phthalocyanine and axially coordinated CO and CH3OH molecules (R4Pc)Ru(CO)(CH3OH), R4Pc2− is tetrakis-(1,4,7,10,13-pentaoxatridecamethylene)phthalocyaninate ion in the presence and absence of ferrocene were studied. The nature of the optical absorption within the near IR region in composites prepared from PVC and (R4Pc)Ru(TED)2 (TED is triethylenediamine) and (R4Pc)Ru(CO)(CH3OH) is discussed. It was established that the photoelectric, non-linear optical, and photorefractive properties of the polymer composite are determined by supramolecular ensemble composed of Ru(II) crown-phthalocyanines.

Photorefractive and nonlinear optical properties of indium(III) tetra(15-crown-5)phthalocyaninate-based composites

Photoelectric, nonlinear optical, and photorefractive properties of hybrid composite materials based on polyvinylcarbazole (PVK) and indium(III) 2,3,9,10,16,17,23,24-tetra(15-crown-5)phthalocyaninate [(15C5)4Pc]In(OH) are studied in detail. Field dependence of the quantum efficiency in a 7.8 μm-thick layer containing 5 at % [(15C5)4Pc]In(OH) is measured. The best approximation of the quantum efficiency with Onsager’s equation corresponds to a quantum yield of thermalized electron-hole pairs φ0 = 0.01 at initial separation r0 = 9.8 Å. Z-scan measurements in a nanosecond range showed that the electric susceptibility of [(15C5)4Pc]In(OH) solution in tetrachloroethane (TCE) with a concentration of 7 × 10−4 mol/L is χ(3) = 1.34 × 10−9 esu. The maximum coupling gain coefficient found for the material composed of PVK and 5 wt % [(15C5)4Pc]In(OH) at an electric-field intensity of 200 V/μm is Γ = 80 cm−1, and the difference between the coupling gain and absorption coefficients is Γ − α = 70 cm−1. The dependence of the coupling gain coefficient on the intensity ratio of interfering beams 1 and 2 (β = I1(0)/I2(0)) in a composite containing 3 wt % [(15C5)4Pc]In(OH) is measured. An increase in β was attained by decreasing intensity of the signal beam I2(0) at constant intensity of the pump beam I1(0) = 0.15 W/cm2 and E0 = 214 V/μm. Within the initial segment of the curve, the coupling gain coefficient increases from 30 to 60 cm−1; then, the coefficient drops almost to the initial value. The data obtained show that the composite materials studied can be used in practice for correcting faded images. The combined analysis of the results obtained and similar data for gallium and ruthenium tetra-15-crown-5-phthalocyaninate complexes revealed the regularities in the change of the quantum yield of thermalized electron-hole pairs and the photorefractive coupling gain coefficient in a series of complexing metals: gallium(III), ruthenium(II), and indium(III). An increase in the molecular weight of the central metal atom is found to result in a substantial decrease in Γ and φ0 due to the increase in the spin-orbit coupling constant.