Jaroslaw Zieba

Temperature-dependence studies of photorefractive effect in a low glass-transition-temperature polymer composite

The temperature dependence of the photorefractive effect in a polymer composite containing poly(9-vinycarbazole), tricresyl phosphate, buckminsterfullerene, and 4-(N,N- diethylamino)-β-nitrostyrene is presented. The photoconductive, electro-optic and photorefractive properties of the material have been studied in the temperature range of 22–61 °C. An apparent increase of electro-optic modulation with temperature and its eventual saturation is observed. This behavior is attributed to the temperature activated orientational mobility of the second-order nonlinear chromophores. The polarization anisotropy between the p- and s-polarized readouts is consistent with what would be expected on the basis of directly measured effective electro-optic coefficients. By correlating the electro-optic value with the diffraction efficiency, the temperature dependence of the space-charge field is obtained and explained by temperature dependencies of the dark conductivity and the photoconductivity of the material.

Dynamics of photorefractive grating erasure in polymeric composites

Theoretical and experimental studies are presented of the dynamics of photorefractive grating erasure in polymeric photorefractive materials with hole traps. A bi-exponential decay for the rate of optical erasing of the space-charge field has been obtained by theoretical solution. The optically induced erasure rate for polymeric photorefractive materials is theoretically predicted to depend on optical intensity as a sublinear relation of Iα, in which α is dependent on the electric field. The characteristics of the traps in a photorefractive material play a key role in the dynamics of grating erasure. Experimentally studied was the dynamic process of erasing the photorefractive grating in a polymeric composite, poly-N-vinylcarbazole:fullerene:diethyl aminonitrostyrene:tricresyl phosphate. The theoretical analysis and experimental results reveal that shallow traps are dominant in this photorefractive material.

Enhanced photorefractive performance in a photorefractive polymeric composite

We characterize the photorefractive behavior of a photorefractive multicomponent polymer composite of PVK‐TCP:C60:DEANST. Efficient plasticization of the host polymeric matrix and utilization of a nonlinear chromophore with a large dipole moment provide a large poling‐induced electro‐optic coefficient. Diffraction efficiencies as high as 40% and asymmetric net two‐beam coupling gain coefficients in excess of 130 cm−1, surpassing those of known inorganic single‐crystalline photorefractive media, are reported.

Two-photon induced fluorescence behavior of DEANST organic crystal

Abstract Temporal, spectral, and intensity-dependence behaviors of two-phonon induced fluorescence emission in the DEANST [4-(N,N-diethylamino)-β- nitrostyrene] organic crystal have been investigated by using 1.06 μm pump pulses from a Q -switched Nd:YAG laser. Both the response-retardation time and the tail-decay time of the two-photon induced flourescence signal are less than 1.5 ns, the temporal resolution of our measurement system, with respect to a given pump laser pulse. The fluorescence signal exhibits a square-low dependence of the pump intensity. At the highest pump intensity determined by the sample damage, the two-photon pumped fluorescence intensity is much higher than the corresponding one-photon pumped fluorescence intensity. Also at the highest pump intensity level, the two-photon induced fluorescence intensity from a 1.2 mm thick DEANST crystal is 7.7 times stronger than that from a 1 mm thick liquid cell filled with Rhodamine-6G methanol solution of ≈ 2 × 10 -3 M concentration. Thus, a high quality DEANST crystal is quite a promising organic crystal for two-photon pumped laser devices or frequency upconversion detection.

Nonelectrooptic nonlocal photorefractive effect in a polymer composite

The grating spacing dependence of photorefractive diffraction efficiency in an organic polymer composite is presented and discussed. The analysis of the grating spacing dependence of the refractive index modulation with the standard model of photorefractive grating dynamics is shown to lead to inconsistencies in determination of the maximum attainable index change. It is shown that the effects resulting from orienting of the composite’s optically second‐order nonlinear chromophores in the periodic local field affect the formation of the refractive index grating.

Photorefractivity in polymeric composite materials

The results of photorefractivity studies in newly developed polymer composite C60/PVK/DEANST are presented. The composite contains fullerene (C60) photosensitizing molecules, second-order active molecules of diethylaminonitrostyrene (DEANST) and charge transporting polymeric matrix of poly[N-vinylcarbazole] (PVK). Photorefractive properties of the material were investigated using erasable volume holography and two-beam coupling techniques. Additional information was obtained from the results of photoconductivity, electro-optic modulation and the angular dependence of holographic diffraction. The kinetics of the effect, as well as the writing beams and the external dc field switching of the refractive grating are discussed. A previously developed theory of space-charge field gratings formation in photoconductive polymers is used to calculate four-wave mixing diffraction efficiency.

Sol-gel-processed inorganic oxides: organic polymer composites for second-order nonlinear optical applications

A new class of promising composite materials consisting of sol-gel processed inorganic oxides and organic polymers has been developed over the last several years. These materials have been shown to be homogeneous, mechanically stable and have excellent optical properties. Second-order nonlinear optical properties are dependent upon the active chromophore being aligned within the structure. We report here the studies on the second-order nonlinear optical properties of a new oxide:polymer composite. A second-order chromophore, (N,N- diethylamino-((Beta) )-nitrostyrene or DEANST) has been doped into a sol-gel/polymer composite comprised of polyvinylpyrrolidone (PVP) and silica. The removal of solvent from a simple sol-gel preparation causes a tremendous shrinkage of the pores of the matrix. In addition, this particular polymer is capable of being crosslinked at elevated temperatures. These two effects were used to retain the alignment of the chromophores within this unique host material. The second-harmonic generation technique was used as a function of time to ascertain the utility of this approach and to determine the precise roles of processing conditions and components necessary to bring about this effect. The results of this work indicate that this composite can preserve the alignment of DEANST to satisfactory levels, making it an excellent candidate for device applications.

New photonics media prepared by sol-gel process

It is recognized that the earliest and most prodigious development in photonics technology will be in the area of second-order nonlinear optical processes: second-harmonic generation and electro-optic modulation. Photonics applications will undoubtedly involve an integration of fast and reliable high-speed optical crossbar switches, electric field sensing devices, and beam alignment of read-write heads for optical data storage in optical computers. The requirements for such devices are very rigorous, and their development relies on employing photonics materials whose linear and nonlinear optical properties can be engineered. There are several organic materials that are being developed into viable devices due to the fact that their (chi) (2) nonlinearities are much higher than those of existing dielectrics. The most recent materials applied to integrated optics have been the sol-gel processed glasses and glass/polymer nanocomposites which have the inherent advantages of being more easily processed and are cost effective. We report in this paper the recent developments of studies involving linear and nonlinear optical properties of some novel sol-gel processed inorganic oxides/organic polymer composites for nonlinear optics and photonics applications.

Photorefractivity in polymer composites

We report on the results of studies of photorefractive properties of a multicomponent polymer composite of PVK-TCP:C60:DEANST. Efficient plasticization of the host polymeric matrix with the TCP agent and utilization of a nonlinear chromophore with large dipole moment allow for achieving large poling-induced electro-optic coefficient. Diffraction efficiencies exceeding 40% and stationary nonreciprocal net two-beam coupling gain coefficients in excess of 100 cm-1, surpassing those of known inorganic single- crystalline photorefractive media, are reported. Dependency of the kinetics of photorefractivity in the composite on external electric field and writing beams fluencies is discussed. An example of holographic recording and retrieval of an image of the standard USAF optical resolution target is also demonstrated.

Polymeric composite photorefractive materials for nonlinear optical applications

Polymeric composite materials constitute a new and very promising class of photorefractive materials. In the design of polymeric photorefractive materials we use multicomponent composites in which necessary functionalities can be independently optimized. The investigated composites consisted of charge transporting polymeric matrix, and optically second-order active molecules. Two different photosensitizers were used to vary the wavelength response. Photorefractive properties of these materials were investigated using erasable volume holography in a non-degenerate four-wave mixing geometry and two-beam coupling techniques. A previously developed model of space-charge field grating formation in photoconductive polymers was used to explain the field dependence of four-wave mixing diffraction efficiency. The model takes into account the field dependence of charge photogeneration quantum yield, carrier field mobility, and electro-optic coefficient. Necessary information about these parameters was obtained from the results of photoconductivity and electro-optic modulation experiments. Special attention was focused on the kinetics of photorefractive response in the composite for optical signal processing and optical storage. It was found that a very effective switching of diffraction efficiency induced by dc electric field occurs in this system. Also, the results of kinetic studies of the index grating writing and its subsequent light-induced erasure, as well as a demonstration of the holographic image recording and retrieval, are reported.