Optical phase conjugation by degenerate four-wave mixing in basic green 1 dye-doped gelatin film using He–Ne laser

Optical phase conjugation in gelatin film doped with basic green 1 has been measured using CW laser radiation (λ=632.8 nm) generated by He–Ne laser of total power 35 mW. The degenerate four-wave mixing (DFWM) experiment allowed for measurement of phase conjugate reflectivity as a function of dye concentration, backward beam intensity, forward beam intensity, probe beam intensity, mean pumping beam intensity and angle between the forward pumping beam and probe beam. For 1 mM concentration of basic green 1-doped gelatin film, 0.1% phase conjugate reflectivity has been observed.     

Vibrational Analysis of Coherent Anti-Stokes Resonance Raman Spectra from Bacteriorhodopsin Containing Isotopically Substituted Retinal Chromophores

Vibrational spectra recorded by coherent anti-Stokes resonance Raman scattering (CARS) from bacteriorhodopsin (BR) samples containing isotopically substituted (²H and ¹³C) retinal chromophores were measured using high repetition rate, low-power, picosecond pulsed excitation (λ₁=580 nm and λ_s=640±3 nm). These picosecond resonance CARS (PR/CARS) data were analyzed via third-order susceptibility relationships [χ ^{( 3 )} ] to obtain band origins, bandwidths, relative intensities, and electronic phase factors assignable to all significant vibrational Raman features in the 1490–1700 cm⁻¹ wavenumber region (the ethylenic stretching and C = N–H rocking or Schiff base modes). Isotopic substitution selectively places ²H at C₁₅, ¹³C singly at the C₁₀ position and at the C₁₄ position, and ¹³C simultaneously in positions of C₁₄ and C₁₅. Each isotopic BR sample was examined not only in H₂O, but also in D₂O, which places a ²H at the Schiff base nitrogen of the retinal. In addition, PR/CARS data were recorded from each isotopic BR sample following either light adaptation [i.e. the BR sample contained a single retinal isomer (all- trans , 15- anti or BR-570)] or dark adaptation [i.e. the BR sample contained a mixture of comparable amounts of retinal isomers (BR-570 and 13- cis , 15- syn or BR-548)]. Excellent agreement was found between the vibrational features observed by PR/CARS and those obtained from spontaneous resonance Raman measurements from the same isotopically substituted BR pigments. Several new vibrational features were also found from the PR/CARS data. Vibrational Raman data from three of the isotopic BR samples in D₂O are reported for the first time.     

The upper limit of the branching ratio for radiative beta decay of free neutrons

We conducted an experiment on radiative neutron beta decay on an intensive cold-neutron beam at ILL during April and May 2002. This work is dedicated to the analysis of the methodology and the results of the study. The main outcome of this experiment is the branching ratio (BR) for the rare neutron-decay mode in the gamma-ray quanta energy region from 35 to 100 keV. The limit obtained is BR<6.9×10^?3 (90% C.L.), which is only a few permilles greater than the theoretical BR value calculated within the standard weak-interactions model.     

Ce：Fe：LiNbO3晶体的全息存储和相位共轭特性的研究

本文用提拉法从熔体中生长了Ce:Fe:LiNbO_3晶体,并采用二波混合和简并四波混合方法研究和测试了晶体的全息衍射效率和相位共轭反射率.以Ce:Fe:LiNbO_3晶体作为存储元件和相位共轭镜,实现了光学实时全息关联存储.     

细菌视紫红质高分辨图象存储中吸收和散射现象的实验研究

本文利用细菌视紫红质变种材料BR_D96N的基态和M态实现了图象的高分辨存储.实验研究了该样品的吸收特性;在此基础上分析了散射光对BR膜图象质量的影响,并通过合理的控制激发光强和激发时间在BR膜样品上得到分辨率为800lp/mm的高分辨图象.     

Polarization-sensitive diffractive optical elements fabricated in BR films with femtosecond laser

Multi-photon product (F₅₄₀-state) of bacteriorhodopsin (BR) polymeric films excited by femtosecond laser shows permanently photoinduced birefringence and dichroism. Based on this property, polarization-sensitive diffractive optical elements (PDOEs), e.g., gratings, two-dimensional optical lattice, Bessel zone plate, were firstly fabricated and investigated in BR films by femtosecond laser multi-beam interference with rotationally symmetric pyramid lenses. These fabricated PDOEs are completely stable at room temperature. The dependence of diffraction efficiency on the incident polarization state was measured. The micro-structures of PDOEs were observed under polarization microscope, and the selective readout diffraction patterns from the polarization-multiplexed PDOEs were demonstrated.     

野生型细菌视紫红质薄膜光谱响应特性的实验研究

细菌视紫红质 (Bacteriorhodopsin ,简称BR)是嗜盐菌细胞膜内的一种光敏蛋白质。BR薄膜材料具有优异的光循环特性和光致变色特性 ,在光信息处理领域中有广阔的应用前景。文章通过紫外 可见光光纤光谱仪测试野生型细菌视紫红质 (BRWT)在经过 5 32nm的YAG激光的泵浦激励后 ,薄膜对探测光的吸收光谱变化情况来着重讨论BRWT的光谱响应特性。采用的样品基态 (B态 )最大吸收波长均为 5 6 2nm ,光密度分别为OD(WT1) 562nm=2 0 4 ,OD(WT2 ) 562nm =1 37。实验结果表明 ,在 5 5 0～ 6 5 0nm波长范围内 ,两个BRWT分子膜对探测光随着探测时间的延长均出现吸收增强的现象。利用双e指数曲线拟合方法分析出 5 5 0～ 6 5 0nm吸收增强的变化过程分为快过程和慢过程 ,其对应的时间常数BRWT1分别约为 11ms和 6 0s ,BRWT2 分别约为 2 4ms和 35s。     

SBN:Cr晶体的光折变四波混频相位共轭特性实验研究

从实验上研究了同成分SBN:Cr晶体在He-Ne激光照射下的四波混频相位共轭特性.首先测量了在不同泵浦光与信号光光强比m及不同光束夹角2θ的情况下,晶体的四波混频相位共轭反射率R随泵浦光强比p的变化关系.其次测量了泵浦光束与信号光束耦合方向对SBN:Cr晶体的四波混频相位共轭特性的影响,并就两种不同掺杂浓度的晶体样品进行了对比,所得实验结果与理论分析基本一致.最后,利用SBN:Cr晶体四波混频相位共轭特性进行了图象畸变消除实验.     

Latest results from Double Chooz

Double Chooz is a short-baseline neutrino disappearance experiment. It detects ν? _e produced in the power plant of Chooz, France, where is located. The main goal of the experiment is the measurement of θ₁₃ mixing angle and in 2011 for the first time the experiment observed an indication for a non zero value of such an oscillation parameter. The mixing angle was successively measured using only the far detector finding the best fit value of sin²(2θ₁₃) = 0.090 _?0.029 ^+0.032 . The near detector is under construction and will start data taking by the middle of 2014 allowing the reduction of the systematic errors. In this paper I make a review of the Double Chooz experiment, focusing in particular on the latest results of the measurement of the mixing angle θ₁₃ relying on the neutron absorption on Gadolinium. I also present results proving the capability of Double Chooz to identify the ortho-positronium. This has been done in an event-by-event basis for the first time in a large liquid scintillator experiments, and can be an additional handle for the electron/positron discrimination in future detectors based on such technology.     

Influence of auxiliary violet light on holographic kinetics at low and high recording intensities in bacteriorhodopsin film

The photochromic bacteriorhodopsin (BR) film can be used as a rewritable holographic recording medium. Due to the saturation absorption and the scattering and reflecting lights from the BR film, the grating contrast-ratio of the hologram is diminished during the hologram recording. When the intensity of the recording light is low, the influence of the saturation absorption and the scatter and reflection of BR film on the grating contrast-ratio is weak. But for the case of intense recording light, this influence is more serious. It is found that the influence of the auxiliary violet light on the holographic kinetics of diffraction efficiency is distinct under different recording intensities. At the low recording light intensity, the steady diffraction efficiency is increased and the peak diffraction efficiency is suppressed by the auxiliary violet light. But for intense recording light, the steady diffraction efficiency and the peak diffraction efficiency are both increased by the auxiliary violet light. Based on the two-state model of BR photochromism, we give a good theoretical explanation to the above phenomena.     

细菌视紫红质膜快速光开关的实验研究

建立了“脉冲激光－连续探测光－连续擦除光”的实验系统。在532nm的调Q脉冲激发光和不同波长的连续探测光作用下，研究了细菌视紫红质（BR）膜的光循环过程中的快速响应特性及各中间态的快速光吸收特性。观察到了微秒量级的快速光开关现象，并分析了激发光脉冲作用结束时，各中间态上细菌视紫红质分子的分布。     

Preparation of sol-gel ZrO2-SiO2 highly reflective multilayer films and laser-induced damage threshold characteristic

Sol-gel (ZrO₂/SiO₂)¹² ZrO₂ films were prepared by spin coating method. The reflectivity spectrum of the films was measured with a Lambda 900 spectrometer. In order to investigate laser-induced damage threshold (LIDT) characteristic of highly reflective films, one-layer ZrO₂ and SiO₂ films, two-layer ZrO₂/SiO₂ and SiO₂/ZrO₂ films were also prepared by spin coating method. LIDT of each film was measured. Damage morphology after laser irradiation was characterized by optical microscopy (Nikon E600K). The experimental results showed that the reflectivity of (ZrO₂/SiO₂)¹² ZrO₂ film at 1064 nm and 355 nm wavelength is 99.7%. The LIDT results decreases as the number of layer of films increases. All the films have similar damage morphology. The experimental results are explained by the different temperature profiles of the films.     

Studies on behaviors of dipalmitoylposphatidylcholine and bilirubin in mixed monolayer at the air/water interface

Mixed monolayers of dipalmitoylposphatidylcholine (DPPC) and bilirubin (BR) were prepared on different subphases. The properties of DPPC/BR monolayer, such as collapse pressure (π_coll), limiting area per molecule (A_lim), surface compressibility modulus, free energy (ΔG_mix) and excess free energy (ΔG_ex), were investigated based on the analysis of the surface pressure-area isotherms on pure water. The results showed that DPPC and BR were miscible and formed non-ideal mixed monolayers at the air/water interface. With the molar fraction of BR (X_BR) increasing, the LE-LC coexistence region of DPPC monolayer was eliminated gradually. The DPPC/BR complex (M_D-B) of 1:2 stoichiometry formed as a result of the strong hydrogen bonds between the polar groups of DPPC and BR. The studies of effects of pH values and calcium ions in subphase on the DPPC/BR monolayers showed that the mixed monolayer became expanded on alkali aqueous solution and on 1 mmol/L CaCl₂ aqueous solution. The orientation of DPPC and BR at air/water interface was also discussed.     

Long holographic lifetimes in bacteriorhodopsin films

The D85N genetic variant of bacteriorhodopsin (BR) displays a nearly permanent lifetime of the photochromic P(490) state. We present pump-probe measurements that demonstrate this behavior. However, diffraction efficiency measurements made from holograms recorded in a hydrated D85N film show markedly different decay behavior, suggesting that a molecular diffusion process is occurring in the film. Holograms recorded with different grating frequencies display correspondingly different decay times, thus supporting this hypothesis. A thin D85N film was fabricated that was chemically cross linked, resulting in the elimination of diffusion of BR molecules within the polymer matrix. This film exhibits a grating lifetime of the order of weeks or more, thus permitting the long-term holographic storage of information.     

菌紫质薄膜光致折射率变化的理论计算和实验测量

基因改性细菌视紫红质BR-D96N由于M态寿命的延长而具有显著的光致变色特性.根据Kramers-Kronig变换关系,样品吸收光谱的变化会引起样品折射率的变化.本文首先从实验上测量了BR-D96N薄膜样品在光激发前后的吸收光谱,然后根据Kramers-Kronig变换关系,理论计算了对应此光致变色光谱变化的光致折射率变化光谱.实验上为了直接测量样品的光致折射率变化,采用Michelson干涉方法测量BR-D96N薄膜在不同探测波长下的光致折射率变化量,并与理论计算曲线进行了比较.     

On the influence of free-carrier scattering mechanisms on semiconductor thin-film plasma spectra

IR plasma reflectivity spectra of semiconductor epitaxial layers on transparent substrates have been calculated by using a modified Drude dielectric function including a frequency-dependent relaxation rate of the form γ(ω) = γ₀+bω². Due to multiple reflections within the semiconductor film, weak structures in the bulk reflectivity spectra are enlarged in the film spectra. The sensitivity of the film reflectivity to variations of the relaxation rate is much larger than the bulk reflectivity for frequencies above the plasma edge and consequently this type of measurement is a very promising method for obtaining information about the scattering mechanisms of free carriers.     

Magnetic ordering in a [Fe/Co]<Subscript>35</Subscript> BCC film studied by nuclear resonant reflectometry

An analysis of the angular dependences of nuclear resonant reflectivity time spectra for different models of magnetic ordering in films reveals an ambiguity in the magnetization direction determined from spectra measured at one orientation of the sample. This analysis explains features in the spectra of the nuclear resonant reflectivity from a MgO/[Fe(6 ML)/Co(3 ML)]₃₅/V (1 nm) film measured before and after sample rotation by 90° about the normal to the surface. It is shown that the spectrum measured only at one orientation of the sample determines only the effective azimuth angle of magnetization γ^eff. This does not exclude the occurrence of a domain structure, while the angle γ^eff does not correspond to the true direction of the preferred orientation of magnetization. The results of measurements at two orientations of the sample can be satisfactorily matched using a model that considers a coherent mixture of states with magnetization directed along the 〈110〉 axis (77%) and with a chaotic orientation of the magnetic hyperfine field B _hf in the film plane for the other nuclei.     

Nonlinear optical studies in tetraphenyl-porphyrin-doped boric acid glass using picosecond pulses

We report the results of our studies on the nonlinear optical response of thin films of tetraphenyl porphyrin doped in boric acid glass for picosecond-duration pulses. The fluence-dependent transmission measurements show that the sample exhibits reverse saturation behavior at 532 nm and saturable absorber action at 683 nm. By fitting the nonlinear transmission data at these wavelengths to a rate equation model, values for σ^S _e and σ_L the excited singlet and ground state cross sections were obtained. The large value (≈8) for σ^S _e/σ_L makes it a potential material for optical limiting at 532 nm, whereas at 683 nm the ratio σ_L/σ^S _e≈4.3. Intensity dependence of degenerate forward four-wave mixing at 683 nm was also investigated to establish the order and magnitude of the nonlinearity. The forward four-wave mixing signal at 683 nm showed a cubic dependence on the input intensity, establishing the third-order nonlinearity. A value of 4×10^-12 esu for the third-order susceptibility |χ⁽³⁾| was estimated from the measured efficiency. The time response of the nonlinearity was measured by the pump-probe transmission experiment, resulting in a decay constant of about 1.8 ns for the repopulation of the ground singlet state at 683 nm. Received: 13 April 2000 / Published online: 20 September 2000     

不同记录光强下辅助紫光对菌紫质薄膜全息衍射效率的影响

具有光致变色效应的菌紫质薄膜可用作可擦重写型全息记录介质. 在全息记录过程中,由于菌紫质薄膜对记录光的散射和反射引起记录光栅对比度下降,当记录光较弱时,这种影响较小,可以忽略;但当记录光较强时,散射和反射光对记录光栅的影响很大,必须考虑它们对光栅对比度的影响才能对实验结果进行合理的解释. 实验发现在不同的记录光强下辅助紫光对衍射效率动力学曲线的影响不同,当记录光强较弱时,加入辅助紫光可以提高衍射效率的稳定值、抑制峰值;而当记录光强较强时,加入辅助紫光除了提高衍射效率的稳定值外,还可以提高衍射效率的峰值. 关键词： 菌紫质 衍射效率 干涉条纹对比度     

Optical reflectivity of (SN)x-single crystals

The optical reflectivity of (SN)_x single crystals was measured in the visible region and the near infrared with light polarized parallel and perpendicular to the polymer chain axis. Whereas the reflectivity for light polarized perpendicular to the chain axis is approximately constant in this region, the reflectance for light polarized parallel to the chain axis exhibits a pronounced plasma edge at 2.72 eV. A simple Drude model was used to analyse the data. Differences between these results and those of previous film measurements are discussed.