V. V. Savel'ev

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.

Photorefractive Polymer Composites based on Third-Order Nonlinear Optical Chromophores

Photorefractive materials based on unplasticized polymers that have a high glass transition temperature and the frozen random orientation of chromophores are prepared by layer casting. Under these conditions, only the third-order susceptibility has a nonzero value, by increasing with an increase in the conjugation chain length and reaching considerable values in the case of nano-sized molecules, such as single wall carbon nanotubes. In single wall carbon nanotubes containing poly-N-vinylcarbazole, the photoelectric sensitivity and photorefractive characteristics are measured at 1064 and 1550 nm.

Second harmonic generation in polymers containing dithiosquarylium dye

Polymer layers containing the dye 2,4-bis(1,3,3-trimethyl-2-indolinylidenemethyl)-1,4-dithiosquaraine display second-order nonlinear optical properties. Depending on conditions of preparation of the layers, the monomer form of the dye or the intermolecular charge transfer complex between two dye molecules are responsible for the second harmonic generation.

Photorefractive Properties of a Polyimide Containing Thiacarbocyanine Dye J-Aggregates

The photorefractive properties of a polyimide containing J-aggregates of a thiacarbocyanine dye were examined. Measurements were made with a holographic apparatus at Ar–Kr laser wavelengths of 647 and 514 nm. The J-aggregate and the monomeric form of the dye, respectively, are responsible for the photoelectric sensitivity at these wavelengths. It was shown that the J-aggregates are also responsible for the nonlinear optical properties of the polymeric system. The combination of these features determines the photorefractive characteristics of the polymer composite: under interference conditions, the intensity of one of the interacting beams (signal beam) increases at the expense of extinction of the other (pumping) beam. The difference between the beam-coupling gain coefficient Γ and the absorption coefficient α increases at 647 nm from 217 to 361 cm–1 with the increasing strength of a constant electric field E0 applied to the layer from 16 to 123 V/μm. Only the samples containing J-aggregates display the photorefractive effect at 514 nm.

Photorefractive Properties of Photochemically Modified Poly(hydroxyaminoether)

The exposure of photosensitive poly(hydroxyaminoether)-based polymer compositions to light leads to the formation of an image with nonlinear optical and photoelectric properties and, hence, photorefractive behavior. Using the holographic birefringence technique, it was shown that the pumping of one of laser beams (signal beam) at the expense of the intensity of another (reference beam) takes place in the photochemically modified regions of the polymer layer. Unlike the majority of the previously studied photorefractive polymeric media, the beam-coupling gain coefficient Γ(cm–1) exceeds the absorption coefficient α(cm–1); i.e., the intensity of the signal beam after passing the layer becomes higher than that before the layer. A net internal gain, i.e. the difference Γ – α, of 117 cm–1is achieved at E0= 26 V/μm. The photorefractive effect is absent from the unexposed areas of the layer.