A simple, convenient and low cost chemical synthesis technique, chemical bath deposition, are used to deposit cadmium sulfide (CdS) and cadmium selenide (CdSe) quantum dots on glass substrates. Based our characterizations, high quality CdS and CdSe thin films have been deposited on the substrates. In order to synthsize CdS quantum dots on glass, we use cadmium sulfate (CdSO4), ammonia water (NH4OH) and thiourea (CS(NH2)2) as reaction agents. For CdSe thin films, we use cadmium acetate as cadmium ion source and sodium selenosulfate / thiourea as a selenium / sulfur ion sources. Aqueous ammonia is used as a complex reagent and also to adjust the pH of the final solution. The asdeposited thin films using this technique are optically transparent, adherent, homogeneous and yellowish for CdS and redish for CdSe without powdered precipitation. The deposition can be made at 60 – 70°C under magnetic stirring for all samples. The films have been characterized by X-ray diffraction, scanning electron microscope (SEM), and UV-Vis absorption. The SEM measurements show that the shapes of deposited CdSe nanoparticles on glass substrates can be controlled to exhibit different shapes under different reaction conditions.
Multilayered germanium nanocrystals embedded in silica (SiO2) matrices are fabricated by using the radio frequency magnetron co-sputtering technique. Transmission electron microscopy shows germanium (Ge) nanocrystals are confined in the (Ge+SiO2) layers in the silica thin films. Linear optical absorption coefficients at different wavelengths and the energy gap of the films are calculated based on absorbance measurement data. Photoluminescence emission property is also characterized. Using the open aperture z-scan technique, we have also measured nonlinear absorption and computed the imaginary part of third-order optical susceptibility of these samples.
Polymer/multiple walled carbon nanotube (MWNT) thin films on glass slide substrates have been fabricated by using the spin-coating method. The optical power limiting performance and nonlinear absorption in these films have been characterized experimentally. Transmission electron micrograph and scanning electron microscope (SEM) techniques have been used to investigate the interaction between polymer molecules and MWNTs. SEM images of polymer functionalized carbon nanotubes show that polymer molecules and MWNTs can interact via -stacking to increase solubilization of MWNTs, which can be used to explain the optical power limiting effect. For quantitative comparison of different polymer MWNT thin film performance, the open Z-scan technique is employed to measure nonlinear absorption coefficient and optical power limiting effects of different polymer MWNT thin films.
Cavity enhanced directional resonance has been experimentally observed in single optically-trapped polystyrene particles, which have a size range from 9 μm down to several hundred nm. The higher resonance peaks correspond to longitudinal modes of the directional laser oscillation in a deformed spherical resonator. The lower peaks are attributed to whispering-gallery modes. For a particle with a diameter of approximately 9 μm, the longitudinal mode numbers of the resonator that is responsible for the observed sharp emission peaks are identified using a ray optics model. It is suggested that both directional and whispering-gallery modes can exist in nanometer-scale size resonators. The potential use of such resonant optical cavities in fiber-based optical sensors for chemical diagnostics is suggested. Considerable additional work is required to completely model and measure the observation of effects briefly summarized here.
Thin film electro-optic materials have been synthesized by a novel electrostatic self-assembly (ESA) method. This method allows the molecular-level, layer-by-layer formation of multilayer thin and thick films of alternating anionic and cationic molecules and other materials. We have found that during the adsorption of dipolar molecules from solution to form a single molecular layer, the dipoles align themselves. In a multilayered material, this leads to multiple functionalities that require a noncentrosymmetric molecular structure, such as active optical properties and piezoelectric behavior. Such properties are usually achieved in other materials by electric field poling. In this paper, we describe the precursor molecular chemistries that we have developed to make electro-optic thin films by this method, how the films are formed, the resulting molecular orientation within the film, and measured electro- optic coefficients to date.
Thin film electro-optic materials have been synthesized by a novel electrostatic self-assembly (ESA) method using both manual and automated processes. This paper discusses the reproducibility of such ESA-formed electro-optic thin films formed by both methods. Multiple films were fabricated based on the same layer-by-layer molecular design. They were evaluated using UV-vis spectroscopy and multiwavelength ellipsometry to demonstrate linear growth with the addition of layers, and to measure the thickness of the formed film. Their electro-optic coefficients have also been measured using Mach-Zehnder and Teng and Man approaches. Variations in the properties, including absorption, thickness and electro-optic coefficients, for all of the test samples are reported. We analyze possible causes for such variations, which include time-dependent differences in solution chemistry and differences between manual and automated fabrication processes. We further suggest approaches to both the solution chemistry and thin film design that may be used to limit the effect of such variations on the performance of electro-optic devices.
Thin film electro-optic materials have been synthesized by a novel electrostatic self-assembly (ESA) method. This wet chemistry synthesis method allows the molecular-level, layer-by-layer formation of multilayer thin and thick films of alternating anionic and cationic molecules and other materials. We have found that during the adsorption of dipolar molecules from solution to form a single molecular layer, the dipoles align themselves. In a multilayered material, this leads to multiple functionalities that require a noncentrosymmetric molecular structure such as active optical properties and piezoelectric behavior. Such properties are usually achieved in other materials by electric field poling. In this paper, we describe the precursor molecular chemistries that we have developed to make electro-optic thin films by this method, how the films are formed, the resulting molecular orientation within the film, and measured by electro-optic coefficients to date. We also describe how the ESA process precursor chemistry may be modified to allow the incorporation of noble metal nanoclusters to form flexible thin films with electrical conductivity on the order of that bulk metals. Such conducting films have been used to form electrode layers on prototype electro-optic devices.
Multifunctional organic-inorganic nanocomposites are of considerable interest in photonics, optoelectronics, and biophotonics. This paper will focus on two topics. In the first part of the paper, we will focus on semiconductor nanocluster sensitized photoconductivity and photorefractivity. The results of photorefractivity studies in newly developed polymer composite PVK: TCP: CdS: NPP are presented. The composite contains charge transporting polymeric matrix of poly [N-vinylcarbazole] (PVK), thiocresol capped CdS photosensitizing nanoclusters, and second-order nonlinear optically active chromophore N-(4- nitrophenyl)-L-prolinol (NPP). Efficient plasticization of the host polymeric matrix was achieved with tricresyl phosphate (TCP). The electro-optic modulation, degenerate four-wave mixing (DFWM) diffraction efficiency and two-beam coupling properties of photorefraction were studied. In the second part of the paper, we investigate surface enhanced fluorescence in a silica matrix using dye in close association with silver nanoclusters. To optimize the photonic functions of 4-[N- (2-hydroxyethyl)-N-(methyl) amino phenyl]-4'-(6- hydroxyhexyl sulfonyl) stilbene (APSS) we have utilized the concept of plasmon enhancement, where resonance interaction with nanosize metal clusters enhances the various optical properties. Novel sol-gel processing has produced composites containing APSS and silver nanoclusters. The energy transfer between the plasmon resonance of the silver nanocluster and the excited state of APSS has been demonstrated.
The contradirectional two-wave mixing (CTWM) is studied and compared with the forward two-wave mixing, the results show that the CTWM offers some unique wave-coupling characters, the energy transfer direction in the process of CTWM is not only decided by the sign of the main light induced carries, but also decided by the relative value of every element in the electro-optical tensor.
A mutually pumped phase conjugator is demonstrated with a novel photorefractive crystal of copper-doped potassium sodium strontium barium niobate, in which the beams travel in a geometric path similar to the outline of a sickle. The maximum reflectivity is up to 168%. Faster response times are measured and are also simulated as a function of incident beam power ratio. Four available input geometries are found. The phase conjugation signals exist wide range of angular and position alignment.
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