Time-resolved optical transients in tetragonal BaTiO3

We present and analyze the room temperature (T= 23.5 degrees C) time behavior of the transmitted intensities of polarized light passing through an unclamped (100)-type single crystal of barium titanate (BaTiO3) when subject to a time-dependent, externally applied electric field. To the authors' knowledge, this is the first reported observation and analysis of such time-resolved optical transients. According to a previous [J. Opt. Soc. Am. A 22, 377 (2005)] observation by the authors, this original optical technique can, in principle, be used on 18 out of 20 noncentrosymmetric crystal point groups where the first-order (Pockels) and second-order (Kerr) electrooptic effects coexist. Because of its nondestructive nature, this novel optical method would be a useful tool in other fields of condensed-matter physics in which time-behavior observation and characterization of certain physical parameters of crystals are important.     

Virtual optical experiments. Part II. Design of experiments

In Part I of this study [J. Opt. Soc. Am. A 20, 698 (2003)], we presented a physically rigorous model for simulating optical probing techniques. We now introduce the concept of virtual experiments as the fundamental strategy for analyzing the measurement techniques and for supporting the design of the experiments. Thus a theoretical study of parasitic effects, the accuracy of the experiment, and the optimum probing conditions becomes possible. In our first example of application, free-carrier absorption measurements are discussed. We present quantitative results for the optimum sample geometry and the optimum optical setup. In addition, we demonstrate that backside laser probing, a typical representative of interferometric techniques, provides excellent spatial resolution and constitutes a powerful method to detect hot spots in the investigated sample.     

Photon-echo novelty filter: a unique time-differential sensor of optical wave-front distortion caused by airborne turbulence

To continue our earlier research on the photon-echo novelty filter, we lengthen the novelty filter's response time by 3 orders of magnitude from nanoseconds to microseconds. On the microsecond time scale of airborne turbulence we demonstrate the potential of the novelty filter as a unique time-differential phase sensor. We observe no considerable degradation of the filter's sensitivity and accuracy to as high as 50 and 200 mus, respectively. This result demonstrates that the filter can be continuously tuned with regard to its response time over a wide range. We further apply the novelty filter to the probing of phase distortions of a laser beam going through a He jet. We also investigate issues regarding the operation of the novelty filter to deal with random and spatially nonuniform phase distortion. The relation of the photon-echo novelty filter to traditional double-exposure holography and the role of the time-differential sensor in adaptive optics are discussed.     

Comparison of test images obtained from various configurations of scanning near-field optical microscopes

The characteristics of a few experimental near-field optical microscopes, located in different laboratories, have been compared on the basis of their ability to image a well-defined submicrometer test object.     

Coherent optical signal transferring on request by use of a BaTiO3 crystal

We demonstrate experimentally a setup with which a two-dimensional picture can be transmitted from one plane to another at a signal request of the latter plane and the original picture continues to propagate unhindered along its original direction to the next stage. The setup makes use of photorefractive four-wave mixing and the self-pumped phase conjugation for its operation. Some means for increasing the contrast of the final transmitted image have been discussed.     

Photon-echo novelty filter for measuring a sudden change in index of refraction

An optical novelty filter with phase-conjugate photon echoes is constructed to measure a sudden change in the index of refraction of a transparent medium. This novelty filter is set up as a Michelson interferometer and employs a europium-doped crystal as a phase-conjugate mirror. The filter is sensitive to the sudden change in index of refraction when the phase-conjugate echo experiences a different path length from the first laser excitation pulse in a photon-echo experiment. Using a Pockels cell as a pure phase modulator, we demonstrate that the filter can resolve a sudden phase change occurring on a nanosecond time scale with an accuracy and resolution close to 5°.     

Highly concentrated solvothermal synthesis of sub-10-nm BaTiO3 nanoparticles for optical applications

Single-crystalline barium titanate: BaTiO₃ (BT) nanoparticles (NPs) with sub-10-nm size have been successfully obtained by a highly concentrated solvothermal synthesis using a high concentration of Ba(OH)₂ and a titanium complex. To obtain sub-10-nm NPs, we focused on the gradual increase in the OH^– ion concentration and the decrease in the dielectric constant of solvents, and BT NPs were produced in 1 h even at a low temperature of 200 °C. High-resolution transmission electron microscopy (HR-TEM) observation revealed that the resulting BT NPs were single-nanometer size, consisting of a single-crystalline structure. ¹H-nuclear magnetic resonance (NMR) relaxation time (T₂) and zeta potential measurements demonstrated that our BT NPs had high dispersibility and dispersion stability under acidic conditions. The yellowness index measurements revealed that the BT NPs dispersions exhibited colorless property. The resulting single nanometer-sized BT NPs are promising as high refractive index materials for optical applications due to being dispersed in optical resins.     

Effect of microwave sintering on the structural, optical and electrical properties of BaTiO3 nanoparticles

BaTiO₃ nanoparticles were prepared by high energy ball milling and subjected to conventional and microwave post sintering at 1,000 °C. From the powder X-ray diffraction results, the synthesized material exhibits strong tetragonality with large c/a ratio. Scanning electron microscope results show the formation of tetragonal shaped BaTiO₃ crystals in the nanometer scale and a significant reduction in the particle size for the microwave sintered sample. The reduced d-spacing of 1.741 Å with high crystallinity for the microwave sintered material is revealed by high resolution transmission electron microscopy analysis. Ultraviolet–visible spectroscopy studies confirm the higher optical band gap (E_g) of 4.157 eV for the microwave sintered sample. Microwave sintered sample shows a very high dielectric constant of ε_r = 4,445 with a low dielectric loss as tan δ = 0.0961. Microwave sintered sample exhibit a high polarization maximum of 73 μC/mm² with reduced coercivity to be 0.293 kV/mm.     

纳米BaTiO3的制备及其负载Ni基催化剂的应用研究

采用溶胶-凝胶法制备了纳米BaTiO₃,用纳米BaTiO₃粉体作载体通过浸渍法制备出Ni/BaTiO₃催化剂,并将其用于CO₂重整CH₄制合成气反应,纳米BaTiO₃粉体粒径为25～60nm,颗粒外貌近似球形,其最佳制备条件为:水解用水量10mL,混合溶液pH=4～5,凝胶化温度343K,973K下煅烧处理,在反应温度为1073K,空速12000mL/(h·g·cat)下,Ni/BaTiO₃催化剂可使重整反应的CH₄和CO₂转化率分别达到94.4％和93.3％。     

Cover Picture: Microstructural Comparison of Conventional and Microwave Sintered BaTiO3 (Adv. Eng. Mater. 5/2007)

The cover sheet shows thermally etched fractured cross‐sections of conventional and microwave sintered BaTiO₃. Microwave sintering has a profound effect on the microstructure. Sintering starts earlier and the Curie temperature is influenced. More details can be found in the article by A. Dorner‐Reisel on page 400.     

Combined laser calorimetry and photothermal technique for absorption measurement of optical coatings

To the best of our knowledge, a combined sensitive technique employing both laser calorimetry and a surface thermal lens scheme for measuring absorption values of optical coatings is presented for the first time. Laser calorimetric and pulsed surface thermal lens signals are simultaneously obtained with a highly reflecting UV coating sample irradiated at 193 nm. The advantages and potential applications of the combined technique and the experimental factors limiting the measurement sensitivity are discussed.     

Relationship between parameters of bacteriorhodopsin film and behavior of optical novelty filters

To continue our earlier research on novelty filters in a system of incoherent light [Opt. Lett. 30,81 (2005)], we discuss the relationship between parameters of a bacteriorhodopsin film and the quality of a novelty filter image. For both fixed and moving velocities of the input image, differences in the novelty filter's image as a function of thickness, lifetime of the M state, and molecular concentration are displayed, and the optimal ranges of parameters of the bR film that correspond to the entire novelty filter image and obvious gray-level differences in the image are given. The method can be used to design high-quality novelty filter images in incoherent light systems.     

纳米BaTiO3粉末的制备及烧结工艺的优化

利用溶胶-凝胶工艺制备了成分均匀、尺寸分布窄的BaTiO3陶瓷纳米微粉,分析了AST掺杂、烧结温度和保温时间对BaTiO3陶瓷显微形貌的影响,利用人工神经网络(ANN)BP模型优化工艺参数,获得了具有结构致密dr=98%、粒度均匀dmax/da=1.20、晶粒尺寸da=2μm的BaTiO3陶瓷.     

BaTiO3/CoFe2O4/BaTiO3复合磁电薄膜生长及应力研究

用激光分子束外延（LMBE）设备,在SrTiO3（001）基片上外延生长BaTiO3/CoFe2O4/BaTiO3多层复合磁电薄膜结构。通过反射式高能电子衍射（RHEED）对薄膜生长过程进行原位监测,结果显示,随着CoFe2O4厚度的增加薄膜内应力逐渐被释放,并且应力释放的过程导致了薄膜生长模式的变化。高分辨X射线衍射（XRD）发现,随着CoFe2O4厚度的增加,CoFe2O4对BaTiO3薄膜的张应力逐渐增大,BaTiO3晶胞的c轴晶格常数逐渐变小。理论计算给出了BaTiO3面外晶格常数c随CoFe2O4沉积时间的变化规律。原子力显微镜（AFM）对表面形貌进行表征,进一步证明了复合薄膜生长模式的变化。     

Anisotropic microhardness in single-crystal and polycrystalline BaTiO3

The room-temperature hardness of single-crystal and dense polycrystalline BaTiO₃ was investigated by microindentation. The longer diagonal of the Knoop indenter was oriented either parallel or perpendicular to the poled axis of the material. The hardness of the unpoled sample was isotropic. However, hardnesses in the poled samples were anisotropic, with the highest hardnesses resulting when the longer diagonal was parallel to the poled axis. The hardness anisotropy may be due primarily to residual stresses caused by the piezoelectric coupling effect.     

Transmission- and side-detection configurations in ultrasound-modulated optical tomography of thick biological tissues

Ultrasound-modulated optical tomography of thick biological tissues was studied based on speckle-contrast detection. Speckle decorrelation was investigated with biological tissue samples of various thicknesses. Images of optically absorbing objects buried in biological tissue samples with thicknesses up to 50 mm were obtained in a transmission-detection configuration. The image contrast was more than 30%, and the spatial resolution was approximately 2 mm. In addition, a side-detection scheme along with two specific configurations were examined, and the advantages were demonstrated. Experimental results implied feasibility of applying the ultrasound-modulation technique to characterize optical properties in inhomogeneous biological tissues.     

Parametric experiments and modeling of a cross-flow coalescence filter

Experiments with a cross-flow precoat coalescence filter using a rotor have been performed in a systematic way, using factor design. Variables like rotor speed, density difference between oil and water, different oil qualities, pore size, drop size, effect of tensides, filter depth, and flow rate have been varied. A physical model has been made taking into account drop capture, drainage, and film rupture. This model is compared with an empirical mathematical model using polynomial approximation for three important experimental parameters. Interception is the most important factor for drop capture. The rotor speed and the density difference also have a significant impact on the filter efficiency. When a drop is captured the drainage rate seems to be high enough to reach the critical film thickness during the residence time for the drop in the filter. This is valid at least for smaller drops in all experiments. The film rupture probability is decreased by surfactants like nonylphenols with variable ethylene-oxide chain length, and especially if these have a hydrophil-lipophil-balance (HLB) value in the range of 12–15.