Polarization-dependent diffraction efficiency of a photorefractive volume grating and suppression of this efficiency

In terms of refractive-index ellipsoid of a uniaxial crystal, the relationship between the diffraction efficiency of a volume grating and the polarization state of a readout beam is theoretically analyzed. The direction of a refractive light beam and the corresponding refractive-index modulation will both be changed by a variation of the polarization state. In the polarization state of the readout beam, which may lead to a strong variation in the diffraction efficiency of the volume grating. This kind of polarization-dependent diffraction efficiency of a volume grating in an anisotropic crystal is extremely disadvantageous for some applications. A method to suppress the polarization-dependent diffraction efficiency by use of double volume gratings is presented, and experiments with LiNbO3:Fe crystal are also demonstrated. The experimental results indicate that this method can well suppress the polarization-dependent diffraction efficiency of a volume grating. Furthermore, the diffraction properties of the double volume gratings are almost independent of the polarization state of the readout beam. The relative values of the diffraction peaks are calculated on the basis of the relationship between index modulation and the state of polarization. The experimental values are in good agreement with the theoretical analyses.     

Effective holographic recordings in the photopolymer nanocomposites with functionalized silica nanoparticle and polyurethane matrix

Effective holographic nanocomposites were developed by the surface-functionalized silica nanoparticles and two acrylate monomers/polyurethane (PU) matrix polymer. The functionalization was done with silane compounds carrying long alkyl chain or vinyl group. We evaluated the holographic nanocomposite films by the diffraction efficiency, volume shrinkage, optical loss, and the film morphology. It was found that acrylate monomers/PU system gave higher diffraction efficiency than those of two monomers due to the high refractive index mismatch between the acrylate-rich and PU-rich regions. With the modification of silica particle, up to 35% of particle loading was possible to give a maximum diffraction efficiency of 93.6% for a film of 20 μm in thickness, along with improved refractive index modulation and the sensitivity.     

Acoustooptic interaction in uniaxial gyrotropic paratellurite crystals

An analysis is made of an intermediate mode of light diffraction by ultrasound in a uniaxial gyrotropic paratellurite crystal. A system of coupled wave equations is presented to calculate the polarization and energy characteristics of the diffracted light for the Raman-Nath, intermediate, and Bragg modes of acoustooptic interaction. The diffraction of light propagating at small angles to the crystal optic axis by a slow ultrasonic shear wave propagating along the [110] crystallographic axis is studied. The amplitude-frequency characteristics of a modulator-deflector for optical radiation are investigated. Curves of the diffraction efficiency as a function of the ultrasonic wave intensity are plotted for various acoustooptic interaction lengths. Pis’ma Zh. Tekh. Fiz. 23, 84–89 (January 12, 1997)     

乳化炸药密度对其冲击波感度的影响

乳化炸药的冲击波感度是评价乳化炸药安全性的重要指标。本研究采用隔板试验法测定了不同密度乳化炸药的冲击波感度 ,并分析了乳化炸药的密度对其冲击波感度的影响规律。研究表明 ,在一定范围内 ,随着乳化炸药密度的增大 ,其起爆所需的冲击波强度逐步减小 ,换言之 ,乳化炸药随其密度的增大变得敏感     

Optimal Twist and Polarization Angles for the Reflective Liquid Crystal Light Modulator

Abstract

We determine the twist angle and the input polarization angle that optimize the efficiency, modulation sensitivity, and contrast ratio for the reflective liquid crystal modulators (especially the liquid crystal light valve). If a monochromatic light source is used, and when the input polarization is parallel to the front molecular director of the liquid crystal, the conventionally used 45° twist has a theoretical maximum reflectance of only 81%. However, a 63·6° twist angle yields the highest efficiency (theoretical maximum reflectance of 100%) as well as a higher modulation sensitivity. When the input polarization is not parallel, different options that yield a high efficiency and an increased modulation sensitivity are available. If the light source is not monochromatic but has a narrow bandwidth, the dispersion effect tends to reduce the contrast ratio, so that a tradeoff between contrast and sensitivity must be made. We show that a configuration with 65–75° twist angle has an efficiency close to 100% with continuously increasing sensitivity but decreasing contrast as the input polarization changes from 0° to ?30°.     

Diffraction properties of transmission photorefractive volume gratings in a cerium-doped potassium sodium strontium barium niobate crystal

The diffraction efficiency of volume gratings written by two-wave mixing in a cerium-doped potassium sodium strontium barium niobate (Ce:KNSBN) photorefractive crystal is studied. It is found that the diffraction efficiency strongly depends on the polarization of writing beams and exhibits loop behavior with respect to the fringe modulation. The fringe modulations before and behind the crystal are compared. Modified coupled-wave theory is used to fit the experimental data. This research presents data that are relevant to the application of Ce:KNSBN crystals to holographic recording and optical information processing.     

45m高砖烟囱定向拆除爆破

介绍了定向爆破拆除复杂环境下45m高砖烟囱工程实例。通过适当地提高爆破切口高度,并采取加固爆破切口以下的烟囱壁等措施,解决了无烟囱倒塌足够长度和烟囱后坐的技术问题。同时选择了合理的爆破参数和有效的安全防护措施,使爆破取得了圆满成功。     

Reflective liquid crystal wavefront corrector used with tilt incidence

To allow angular separation of the beam reflected off a liquid crystal wavefront corrector from the incident beam, it is convenient to introduce a small incident angle. This avoids using a beam splitter and the associated energy losses. The effect of the tilt incidence on the liquid crystal wavefront corrector was investigated in this paper. For a parallel aligned liquid crystal wavefront corrector, a simplified model was established and used to analyze the change of the phase modulation under the tilt incidence. The simulated results showed that the effect of the tilt incidence on the phase modulation can be ignored when the angle of tilt incidence is less than 6 degrees. The phase modulation related to the incident angle was measured and the changing trend was similar to the calculated results. The effect of the tilt incidence on the diffraction efficiency of the liquid crystal wavefront corrector was also discussed. The simulated results indicated that the reduction of the diffraction efficiency is less than 1% for incidence angles under 3 degrees. Last, a closed loop correction experiment was done with an incident angle of 1 degrees. After correction, the averaged peak to valley (PV) and root mean square (RMS) of the wavefront were down to 0.15 lambda and 0.03 lambda, respectively, and a resolvable image was acquired.     

Simple method for determining the crystalline axes of nonlinear uniaxial crystal with second-harmonic generation

For uniaxial crystal the optic axis (Z axis) can be determined easily by means of observing its growth pattern or by linear optical methods such as conuscopy. However, determination of the other crystalline axes is not so trivial, normally requiring x-ray diffraction measurements. We propose a simple method for determining the other two axes of the nonlinear uniaxial crystal, using second-harmonic generation. For several uniaxial crystals (with 3m, 62m, 42m, and 32 point groups) the intensity change of the second-harmonic output is calculated as the crystal is rotated azimuthally with respect to the Z axis. The principle is demonstrated in an experiment with LiNbO(3) crystal to determine the X axis with 0.2 degrees accuracy.     

基于光折变光栅的可调谐滤波方案及特性分析

在LiNbO3单模波导上利用双光束干涉可形成光折变波导光栅,针对粗波分复用系统提出了通过实时改变双光束之间的夹角进而改变光栅间距,实现可调谐滤波的方案.利用光折变动力学理论,得到光栅调谐时间在毫秒数量级.研究发现,适当提高光强和增加杂质掺杂浓度可提高衍射效率、减少光栅初次建立时间.基于耦合波理论的数值模拟结果表明,增大光栅长度能使衍射效率提高且带宽变小,而增加折射率调制度使衍射效率提高但同时带宽变宽.在折射率调制度为8×10-5,光栅长度大于12mm时,可获得91％以上的衍射效率和小于0.08 nm的带宽.     

Holographic-recording improvement in a bismuth silicon oxide crystal by the moving-grating technique

We investigate the enhancement of the diffraction efficiency of dynamic gratings recorded in a bismuth silicon oxide crystal at large modulation by the moving-grating technique. The optimum fringe velocity for maximum diffraction efficiency and the degree of enhancement of the diffraction efficiency at optimum fringe velocity are experimentally found to be dependent on the fringe modulation. We apply this technique to real-time incoherent correlation using bismuth silicon oxide. There are two main advantages in using moving gratings: First, the signal-to-noise ratio can be improved considerably because of the improved diffraction efficiency. Second, the resonant effect reduces the effect of environmental disturbances on the peak-correlation intensity, which is significant when the threshold detection level of the correlator is set.     

Critical Edge Characterization of the Optical Tensor of a Uniaxial Crystal

Abstract

The angle dependent reflectivity at the boundary between a uniaxial crystal and an isotropic fluid, which has a refractive index greater than the smaller index of the uniaxial material but less than the other index, is analysed extensively. Consequently the use of a prism and matching fluid with just such refractive indices allows a procedure for the complete characterization of a uniaxial medium to be established. This is undertaken by studying the reflectivity at the prism/fluid/crystal interface with an angle of incidence near to the pseudo-critical angle of the lower index in the uniaxial crystal and examining how the reflectivity varies with the rotation of the uniaxial crystal. Experimental results using a single crystal of calcite give very good agreement with the analysis and computer modelling of this situation and illustrates the use of the new technique.     

阶梯形浮雕和折射率位相光栅的衍射性质比较

位相全息图一般既有浮雕调制又有折射率调制,它们都会对衍射特性产生影响。利用以严格电磁波理论为基础的模式匹配法（ＭＭＴ）,从理论上比较了阶梯形浮雕位相调制光栅和折射率位相调制光栅对ＴＥ波的各级衍射效率。尽管它们同一周期内的相应部分所引起的位相变化相同,但随着光栅层厚度的加大两种位相调制光栅的各级衍射效率会出现差别。这种差别与周期有关。并将矢量理论的结果与标量理论的结果进行了比较,研究结果对研究全息术     

The growth of l-Glutamic acid hydrochloride crystals by Sankaranarayanan-Ramasamy (SR) method

An efficient semiorganic nonlinear optical crystal l-Glutamic acid hydrochloride has been grown by using the novel uniaxial crystal growth method of Sankaranarayanan and Ramasamy with a slight modification in the experimental setup. This method allows the crystals to grow in one specified axis with well developed facet. The grown crystal has a cylindrical morphology with good optical quality. The grown crystal has been characterized by powder X-ray diffraction and UV-Vis-NIR analyses. The NLO efficiency of the crystal has been confirmed by using the Kurtz powder technique.     

Solid lipid nanoparticles of ondansetron HCl for intranasal delivery: development, optimization and evaluation

The present investigation deals with the development and statistical optimization of solid lipid nanoparticles (SLNs) of ondansetron HCl (OND) for intranasal (i.n.) delivery. SLNs were prepared using the solvent diffusion technique and a 2(3) factorial design. The concentrations of lipid, surfactant and cosurfactant were independent variables in this design, whereas, particle size and entrapment efficiency (EE) were dependent variables. The particle size of the SLNs was found to be 320-498?nm, and the EE was between 32.89 and 56.56?%. The influence of the lipid, surfactant and cosurfactant on the particle size and EE was studied. A histological study revealed no adverse response of SLNs on sheep nasal mucosa. Transmission electron microscopic analysis showed spherical shape particles. Differential scanning calorimetry and X-ray diffraction studies indicated that the drug was completely encapsulated in a lipid matrix. In vitro drug release studies carried out in phosphate buffer (pH 6.6) indicated that the drug transport was of Fickian type. Gamma scintigraphic imaging in rabbits after i.n. administration showed rapid localization of the drug in the brain. Hence, OND SLNs is a promising nasal delivery system for rapid and direct nose-to-brain delivery.     

Holographic recording with orthogonally polarized beams in a cesium-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 crystal

Holographic recording with orthogonally polarized beams in a cesium-doped KNSBN [(K(0.5)Na(0.5))(0.2)(Sr(0.75)Ba(0.25))(0.9)Nb(2)O(6)] crystal has been studied. It was found that this kind of photorefractive crystal possesses high linear dichroism, which makes it suitable for use in polarization holography. The diffraction efficiency as a function of the polarization orientation of the reference beam and as a function of the fringe modulation at the optimum polarization orientation of the reference beam is experimentally investigated. Theoretical fitting based on Kahmann models was performed and agrees well with the experimental data. In the experiments, both polarization holography and conventional holography are used to record a binary object. The reconstruction shows that polarization holography with Ce:KNSBN is highly effective, exhibiting high diffraction efficiency and reduced fanning noise.     

Measurements of holographic properties of bacteriorhodopsin films

Several different bacteriorhodopsin (BR) films are characterized with respect to general holographic properties. Experimental measurements include diffraction efficiency and sensitivity as functions of the writing intensity and grating frequency, hologram thermal-decay behavior, diffraction efficiency as a function of the grating tilt within the film and the modulation depth, and estimates of the refractive-index change from the diffraction-efficiency data. The films studied include those made from wildtype BR and the genetic variants D96N and D96N/T46V. The film holographic properties were found to be relatively insensitive to the grating frequency and the grating-tilt angle. The diffraction efficiency dropped off more sharply as a function of the modulation depth than did a purely linear medium, and only the hydrated wildtype film exhibited significant behavior variation with different writing intensities because of its short M-state lifetime. The maximum diffraction efficiency measured was approximately 7.5% for a hydrated D96N BR film. We also find that the hydrated BR films exhibit significantly higher refractive-index modulation than do dry films.     

Conical Diffraction from Uniaxial Gratings

Abstract

We develop a method for solving the problem of conical diffraction at a corrugated interface between an isotropic medium and a uniaxial crystal. The method, based on the Rayleigh hypothesis, is valid for gratings with shallow grooves, arbitrary orientations of the optic axis, and arbitrary orientation of the plane of incidence with respect to the main section of the cylindrical corrugation. The theoretical formalism is applied to model the conversion between polarization states of electromagnetic waves reflected at the sinusoidally corrugated interface between a uniaxial crystal and an isotropic dielectric or metal, for incidences from the isotropic side or the uniaxial one. The combined effect of conical diffraction and material anisotropy on polarization conversion is exemplified in both cases.     

A thermomechanical crystal plasticity constitutive model for ultrasonic consolidation

We present a micromechanics-based thermomechanical constitutive model to simulate the ultrasonic consolidation process. Model parameters are calibrated using an inverse modeling approach. A comparison of the simulated response and experimental results for uniaxial tests validate and verify the appropriateness of the proposed model. Moreover, simulation results of polycrystalline aluminum using the identified crystal plasticity based material parameters are compared qualitatively with the electron back scattering diffraction (EBSD) results reported in the literature. The validated constitutive model is then used to simulate the ultrasonic consolidation process at sub-micron scale where an effort is exerted to quantify the underlying micromechanisms involved during the ultrasonic consolidation process.     

Rigorous analysis of diffraction gratings of arbitrary profiles using virtual photonic crystals

A new approach is developed to calculate diffraction efficiency for a dielectric grating with an arbitrary refractive index profile. By treating a one-dimensional grating as a segment of a virtual two-dimensional (2D) photonic crystal, we exploit a rigorous theory of photonic crystal refraction and calculate the diffraction efficiencies. We expand, analytically in many cases, the dielectric function of the grating into 2D Fourier series. We find the eigenmodes for the virtual photonic crystal, and then use these eigenmodes to match the boundary conditions by solving a set of linear equations. In two such simple steps, the diffraction efficiencies can be computed rigorously without slicing the grating into thin layers.