Formation dynamics of nonvolatile crossed-beam photorefractive gratings in doubly doped LiNbO3 crystals: Theoretical investigation

The formation dynamics of crossed-beam photorefractive gratings formed by the method of two-center holographic recording in doubly doped LiNbO₃ crystals is investigated in this paper based on the theoretical model combining the two-center band transport model with the two-dimensional coupled-wave theory. The numerical simulations are presented for two-center holographic recording crossed-beam photorefractive gratings in LiNbO₃:Fe:Mn crystals. The temporal and spatial evolutions of the refractive index modulation and the diffraction efficiency are shown. The spatial variation of the wave intensity is also presented.     

Exact solution of stationary holographic four-wave mixing in photorefractive crystals: two-level model

Based on the two-level model of recording and read-out of dynamic holographic gratings, precise expressions for wave amplitudes, diffraction efficiency and the gain coefficient representing the generalization of the corresponding formula by Kukhtarevet al. have been obtained. This model allows one to take into account the effect of the read-out beam on the holographic grating and to solve a problem of four-wave mixing in transmission geometry with wave depletion and arbitrary value of the spatial phase shift between the holographic grating and the interference pattern.     

Effect of reflections on phase hologram recording in amorphous As-S-Se films

Experimental and theoretical studies of phase hologram recording in amorphous As-S-Se films with slightly wedge-shaped thickness profile are presented. It is shown that Fabry-Perot resonator effect caused by the interference of multiply reflected light beams inside the sample strongly changes the values of diffraction efficiency and its growth rate as well as the exposure time dependences of diffraction efficiency and transmissivity making them site-dependent and sample-dependent. Absorptivity and recording light intensity inside the sample are also significantly changed. The obtained results can be used to explain the holographic and optical experiments also in other materials with Fabry-Perot resonator effect such as other transparent thin films and photorefractive crystals.     

Nonlinear model of sequential recording of superimposed holographic gratings in photopolymer composites with allowance for the self-diffraction from spatial harmonics

The problems of sequential recording of superimposed holographic diffraction structures of transmission and reflection types in photopolymer composites have been investigated taking into account an arbitrary degree of photopolymerization nonlinearity and the interference pattern contrast at an arbitrary ratio of the photopolymerization and diffusion mechanisms of recording and self-diffraction processes. A theoretical model for N superimposed phase diffraction structures has been constructed by solving interrelated kinetic equations of photopolymerization for H + 1 spatial harmonics of each diffraction structure. This approach makes it possible to investigate the temporal dynamics of the harmonic amplitudes, spatial profile, diffraction efficiency, and angular selectivity of recorded gratings. The model proposed takes into account the diffraction of recording beams from the first harmonic of the ith grating during formation of the (i + 1)th grating.     

On the possibility of distributed associative writing of information by the superimposition of images (plurography)

An expository account is given for the principle of distributed associative writing of optical images by recording in a photosensitive medium the total signal from a set of superimposed images with a random spatial shift. The method preserves the basic characteristic qualities of the holographic method but does not require the use of sources of coherent or monochromatic radiation. The results of an experimental test of the method are presented. Zh. Tekh. Fiz. 68, 98–101 (May 1998)     

Evanescent wave holographic recording in nanosize thick chalcogenide glass films

The results of holographic gratings recording in 29, 15 and 8 nm thick As₂S₃ films are presented in the paper. The method is based on the interference of surface-propagating evanescent waves, created by total internal reflection. The condition for successful recording is the penetration depth of these inhomogeneous waves to be greater than the films thickness. In this case, the film’s refractive index does not affect the total internal reflection (TIR) condition and could be greater than the input glass prism. The experimentally obtained low diffraction efficiencies by this holographic recording technique is due to the very low refractive index modulation, but the good signal-to-noise ratio - better than 50:1 and Bragg-type diffraction are a base for future applications of this grating formation method in nanotechnology.     

Polarization holographic gratings with high diffraction efficiency recorded in azopolymer PAZO

Azopolymers are one of the most efficient materials able to record the polarization state of light. They have numerous applications, such as data storage and diffractive optical elements with unique polarization properties. An essential parameter for each diffractive element is its diffraction efficiency η. In order to optimize the recording conditions and obtain high-efficient polarization holographic gratings, in the present work we study the dependence of the diffraction efficiency on the recording angle and thickness of a series of azopolymer layers. Three recording angles are used ??10°, 20° and 30° and three series of thin films with thicknesses 470, 850 and 2400 nm from the water-soluble azopolymer PAZO. The gratings are inscribed by two plain waves with left and right circular polarization from a He-Cd gas laser (442 nm). The diffraction efficiency of the gratings is probed with a right hand circularly polarized beam from a probe laser with wavelength 635 nm. The kinetics of diffraction efficiency η(t) in the +?1 diffraction order are presented and compared. Our experimental results indicate that highest diffraction efficiency (more than 40%) is obtained for the sample with thickness 2400 nm and for recording angle 10°. As the holographic recording in azopolymers is usually accompanied by formation of surface relief gratings, the surface topography of the recorded samples is also investigated by atomic force microscopy.     

Effect of recording conditions on the anisotropic diffraction of volume holographic gratings

The anisotropic Bragg diffraction of the volume holographic gratings in photorefractive crystals are investigated based on the model of anisotropic coupled-wave theory. The effect of the initial intensity ratio and the recording angles of the two recording waves on the anisotropic Bragg diffraction properties is discussed. It is shown that both the ratio of the initial intensity and the incident angles of the recording waves are selective action for the anisotropic Bragg diffraction efficiency of the volume holographic gratings, while these two recording conditions are not selective action for the isotropic Bragg diffraction. Furthermore, the Bragg phase matching condition of anisotropic diffraction is analyzed when the recording angles change.     

局域体全息光栅衍射的平面波与柱面波的波前转换研究

利用一维耦合波理论研究了入射方向相互垂直的一束平面波与一束柱面波干涉形成光折变局域体全息光栅的波前转换情况。给出了透射波和衍射波振幅的解析表达式。讨论了该局域体全息光栅的几何尺寸以及全息透镜的焦距对光栅衍射效率的影响。结果表明,随着光栅横向尺寸的增加,光栅的衍射效率也逐渐增加。然而,光栅的衍射效率却随着光栅纵向尺寸的增加而减小。全息透镜的焦距越长,光栅的衍射效率也越大。此外,分析了光栅的布拉格选择特性,该光栅具有非常好的角度选择特性。在平面波与柱面波干涉形成全息透镜的设计中,为了获得最优的衍射效率,应当根据要求合理地选择记录所用柱面波和设计光栅的几何尺寸。     

铌酸锂晶体中的磁光折变效应研究

对于掺铁铌酸锂晶体中不同全息记录配置下的磁光折变效应做了比较系统的理论分析，给出了铌酸锂晶体所有的磁光生伏打非零张量元. 详细计算并给出了不同全息纪录配置下的所有体光生伏打、磁光生伏打电流的解析形式. 理论结果表明，由于磁光生伏打效应引起了光激发电流的变化，所以对于每种配置全息光栅的衍射效率都会受到外加磁场的影响；对于不同的全息记录配置，磁场对铌酸锂晶体光折变非线性性质的影响也不同.讨论了一种确定特定张量元的方法. 关键词： 磁光生伏打 磁光折变效应 光生伏打     

大角带宽高衍射效率体全息光栅的设计和制备

高性能体全息光栅是全息波导的重要耦合元件,角带宽小、平均衍射效率不高是制约体全息光栅性能的重要因素.以不对称倾斜记录为出发点,设计并制备了大角带宽高衍射效率的体全息光栅.首先讨论在横电模式光和横磁模式光下体全息光栅的记录参数与其衍射效率的关系,找到平均衍射效率较高的记录参数范围,随后进一步分析在此范围内的记录参数与体全...     

90°全息记录衍射效率分析与提高

对光折变全息记录特别是双中心全息记录中90°记录结构下较低的衍射效率进行了研究,采用局域衍射理论对90°记录结构的衍射进行了分析,表明在同样的折射率变化和2 mm的光束宽度的情况下,只有当折射率光栅振幅大于10^-4时,90°记录结构衍射效率才能够与小角度透射记录结构的衍射效率大致相当。针对环境干扰导致的干涉条纹振动影响光栅记录,提出了有效调制度概念,根据分析90°记录结构的干涉条纹间距很小,容易受外界环境干扰而导致低的折射率变化率,因此应采用主动条纹锁定系统。此外在双中心全息记录中,微观光学参量的优化对衍射效率影响也很重要。     

Dynamics of pulsed recording of holographic diffraction gratings in photopolymer materials

The dynamics of recording holographic diffraction gratings in photopolymer material using 10-ns pulses of Nd:YAG laser radiation (532 nm) was investigated. The formation of permanent and intermediate gratings was observed. Optimization of the photopolymer composition for pulsed recording was performed. The kinetic photopolymerization models taking into account the mechanisms of radical destruction due to recombination and by impurities are verified. Measurement of the recording kinetics at different recording angles showed that diffusion does not affect the hologram formation for times of the same order of magnitude as the recording duration (0.1 s) at a length of the grating half-period. Samples of the photopolymer composition in triethanolamine were investigated and diffusion of oligomeric acrylamide molecules was revealed. The diffusivity was found to be 1.1 × 10^?9 cm²/s.     

全息记录新材料：重铬酸盐—三醋酸纤维素酯

本文报道一种新的全息记录材料：重铬酸盐－三醋酸纤维素酯组成的感光介质。这种全息材料具有较强的实时效应，较高的衍射效率，良好的抗潮能力和环境稳定性等特点。文中分析了这种材料的感光成象机理，通过实验研究了其全息记录特性，给出了实验结果。     

Light diffraction from the volume holograms in electrooptic birefringent crystals

Angular bandwidth of the image reconstructed from the volume phase hologram at a wavelength different from that of the recording beams has been analysed. An optimum holographic scheme on the basis of anisotropic diffraction uniting maximum bandwidth of the Gabor's scheme and advantages of the Leith-Upatnieks scheme has been proposed for non-destructive readout of the volume hologram in birefringent photorefractive crystals. The main results of the theoretical analysis leading to the optimum holographic arrangement for electrically controlled retrieval of information from the volume of the electrooptic crystal are presented. Demonstrating experiments has been performed with LiNbO₃: Fe crystals.     

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     

Holographic investigation of the Ag-As2S3 sandwich-like structure

The evolution of diffracted power is followed in real time during the recording of simple holographic gratings in Ag-As₂S₃ sandwich structures by means of a He-Ne laser. Measurements are made of the kinetics in several diffraction orders in which the holographic exposure is combined with uniform pre- or post-illumination of the sample. The results obtained suggest the presence of two recording mechanisms: one, predominantly phase, due to photodiffusion of silver into the sulphide layer and another, mainly amplitude, due to the bleaching of the silver deposit.     

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.     

（Ce，Cu）：LiNbO3晶体非挥发全息记录理论研究与优化

根据双中心带输运模型，对（Ce，Cu）：LiNbO3晶体双中心非挥发全息记录进行了理论研究与优化。推导了（Ce，Cu）：LiNbO3晶体的微观参量，采用数值方法通过严格求解模拟双中心带输运方程来模拟全息记录过程。分析了记录过程中，记录与敏化光强、Ce和Cu掺杂浓度以及晶体微观参量对（Ce，Cu）：LiNbO3晶体双中心全息记录的影响。发现（Ce，Cu）：LiNbO3晶体非挥发全息记录中实现高衍射效率与固定效率的主导因素是深中心Cu，在记录过程中，深中心Cu建立起了很强的空间电荷场。数值模拟的结果经过实验验证，最高饱和与固定衍射效率别为60．5％和53．8％。