Recording of time-varying electrical signals with one-dimensional holograms

A method of optically recording and reconstructing electrical signals in the form of one-dimensional holograms is described. For this purpose a pulsed laser beam is modulated according to the information to be stored. This beam is superimposed on a spatially and temporally constant reference beam, and the resulting interference pattern is recorded on a film which is moved past the light distribution. The one-dimensional holograms thus recorded appear arranged in narrow tracks which partially overlap.For reconstruction the film is driven past a spatially and temporally constant reconstructing wave. The illuminated holograms reconstruct a closely spaced chain of points which successively pass by a detector in which they produce an alternating current which, after appropriate amplification and filtering, presents the original signal.     

Grain size of MnBi films

MnBi films were prepared by annealing Bi-Mn composite films. The grain size of the MnBi films was strongly influenced by the temperatureT _s of the film substrate during evaporation of Bi and Mn. For 55-nm-thick films, the numberN of MnBi grains per mm² decreased from 4×10⁶ per mm² forT _s =+90°C to 1 per mm² forT _s =−40°C. The diameters of the largest grains observed were about 5 mm. For interpretation of this result, the formation process of MnBi films was observed magneto-optically and electronmicroscopically. It was found thatN was determined by the structure of Bi in the Bi-Mn composite films and that this strongly depended onT _s .     

Localized one-dimensional theory for volume holograms

Coupled partial differential equations are derived, consistent with localized use of one-dimensional theory in a thin volume hologram, from modifications to both one-dimensional and two-dimensional theory. The approximations inherent in the model and the range of validity of the solution are discussed.     

Running holograms in azopolymer films

We report investigations on running holograms recorded in an azopolymer film made of a poly(methyl methacrylate) matrix doped with Disperse Red 1. Two-wave mixing experiments were carried out in the symmetrical transmission geometry. A stabilization technique was employed for active control of the phase shift between the real-time hologram and the interference pattern. Depending on the imposed phase shift, a running hologram propagates in the material in the form of an isomerization wave created by a continuous erasing–rewriting process. Diffraction efficiencies and the hologram velocities were measured as functions of the holographic phase shift at the wavelengths 515 and 488 nm. The experimental results were compared to theoretical curves obtained from a simplified model of the isomerization kinetics. The selective contributions of the phase and the amplitude gratings to the whole hologram were also determined.     

High rotatable magnetic anisotropy in MnBi thin films

The variations of the structural and magnetic properties of Bi/Mn/Bi and Mn/Bi/Mn trilayer film systems of equiatomic composition in the process of vacuum annealing are studied. The annealing of Bi/Mn/Bi films at a temperature of 270°C for an hour results in the synthesis of the well-studied highly oriented low-temperature LT-MnBi(001) phase with the perpendicular magnetic anisotropy K _u ～ 1.1 × 10⁷ erg/cm³ and coercivity H _C ～ 1.5 kOe. In contrast to Bi/Mn/Bi, polycrystalline LT-MnBi nanoclusters are formed in Mn/Bi/Mn films under the same annealing conditions. A high rotatable magnetic anisotropy exceeding the shape anisotropy is detected in the films under consideration: the easy axis of anisotropy with the inclusion of the delay angle in magnetic fields above the coercivity H > H _C = 9.0 kOe can be oriented in any spatial direction. It is shown that the nature of rotatable magnetic anisotropy is due to the structural coexistence of epitaxially coupled LT-MnBi and QHTP-Mn_1.08Bi phases. The reported experimental results indicate the existence of a new class of ferromagnetic film media with the spatially tunable easy axis.     

Recording and reproducing gabor holograms for generating interferograms

The conditions for producing a single-exposure hologram of the focussed image of an amplitude scatterer by the Gabor method, which provide for the generation in diffusely scattered fields an interference pattern typical of the spherical aberrations of lenses, are examined. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 75–80, October, 1996.     

Temperature dependence of magnetic properties of oriented MnBi films

The temperature dependence of the Faraday rotation and the coercive field of oriented low-temperature phase and quenched high-temperature phase MnBi films was measured between 20 °C and 400 °C. A dependence of the Curie temperature of low temperature phase films on the film thickness was found and measured.This work was supported in part by the Bundesministerium für Bildung und Wissenschaft (DV 3.401/T 4.3.2).The author thanks Dr. E. Feldtkeller for valuable discussions.     

Recording volume holograms on color centers in a CaF2 crystal

The conditions for preparing photochromic CaF₂ crystals, recording holograms with 532-nm radiation in them, and postexposure photothermal treatment of samples with holograms that provide the formation of holographic elements of significant thickness (about 1 cm) are considered. It is shown that the diffraction efficiency of volume holograms in such crystals in the case of reading out by radiation with wave-lengths of 532 and 632.8 nm can be as high as 10–15%. The role of the recording mechanism and the Borrmann effect in the fabrication of these holograms is demonstrated.     

Anomalous Hall effect and electron transport in ferromagnetic MnBi films

The electron transport properties of highly c-axis oriented MnBi thin films of various thicknesses have been investigated. Samples are metallic but the low temperature resistivity shows an unusual T(3) dependence. Transverse Hall effect measurements show that both the ordinary and anomalous Hall coefficients decrease with decreasing temperature below 300 K, but the ordinary Hall coefficient (R(0)) undergoes a sign reversal around 105 K, where the magnetic anisotropy also changes sign. Analysis of the Hall data for various samples shows that the anomalous Hall coefficient (R(s)) exhibits a strong ρ(2) dependence, where ρ is the longitudinal resistivity.     

Rayleigh curve and coercive force of thin MnBi films

Statistical Rayleigh-curve theory is applied to thin evaporated MnBi films in order to obtain information concerning the density of wall pinning centra. The treatment results in a prediction of the coercive forceH _c and the average distance between adjacent wall pinning centra, 2L ₀. The coercive forceH _cis also measured experimentally. The results of the two methods are in good agreement with each other. The influence of dislocations on the coercive force is discussed briefly.     

Thickness dependence of temperature coefficient of resistance of MnBi films

In-situ measurements of the temperature coefficient of resistance of electron-beam evaporated MnBi films are reported for the thickness range 30–180 nm. The thickness dependence of the temperature coefficient of resistance curves are plotted for different weight ratios, annealing times and substrate temperatures. The temperature coefficient of resistance shows marked size effect, and is negative for lower thicknesses (<100nm) and positive for higher thicknesses. The experimental data is in good agreement with the Mayadas-Shatzkes theory. The thickness dependence of the Curie temperature also indicates marked size effect.     

Saturation magnetization of MnBi films with different thicknesses and composition

The saturation magnetization of MnBi films in the low-temperature phase and the quenched high-temperature phase was measured at room temperature by a new method recently described. The measurements were performed with samples of varying thickness and composition (ratio Mn:Bi). The results obtained show no dependence either on film thickness or on composition. Hence, the different magnetization values given in the literature for bulk and thin film samples of the quenched high-temperature phase must not be attributed to a thickness dependence of the samples or to stoichiometric variations. This work has been supported by the data processing program of the Federal Department of Research and Technology of the FRG. The authors alone are responsible for the contents.     

MnBi磁性多层膜磁光科尔效应的数值模拟

基于各向异性的平面电磁波传输理论和4×4矩阵法，计算了MnBi，Mn_0.53Bi_0.47，Mn_0.52Bi_0.44Sb_0.04磁性多层膜系列的磁光科尔旋转角、椭圆率随波长、入射角、磁性层厚度变化曲线.计算结果表明，模拟的科尔旋转角、椭圆率随波长变化规律与实验结果吻合很好；在一定波长的垂直入射下，模拟的科尔旋转角、椭圆率随磁性层厚度变化曲线出现科尔谱极大；在磁性层厚度一定的情况下，当入射光以某一角度 关键词： 4×4矩阵法 磁性多层膜 磁光科尔谱 介电张量     

Storage of binary electrical signals in one-dimensional holograms with extremely narrow tracks

A report is given on the results of an experiment in which binary data stored in sequentially superimposed one-dimensional holograms with extremely narrow tracks were recorded on a transported recording medium. The width of the holograms was reduced to 3 μm. Since the results obtained show the optical signal-to-noise ratio of the reconstructed image points to be only slightly inferior to that with holograms with 100 μm wide tracks, the method used can be expected to yield an areal bit density greater than 10⁷ bits/cm².     

Reflection-type polarization holograms in bacteriorhodopsin films for low-light recording

Reflection-type polarization holograms with phase-conjugated readout are very useful for low-light recording with bacteriorhodopsin (BR) films. The dependence of reflection-type holograms with parallel and orthogonal recording beams on their intensity ratio (1:1-1:20) was investigated. It was found that for orthogonally polarized beams the phase-conjugated signal depends significantly less on the beam intensity ratio than predicted by coupled-wave theory. This finding is of particular relevance for recording of very low object-beam intensities with BR films, e.g., in interferometry, where signals with a high signal-to-noise ratio, owing to the different polarizations of the scattered light and the signal, and with low dependence of the diffraction efficiency on the ratio between the reference and object-beam intensities are obtained. With this asymmetric recording process, holograms were recorded successfully in BR films with a good signal-to-noise ratio at exposures (from the object side) as low as 50muJ/cm(2) . These exposures are in the range of those typically used for silver halide films.     

Recording of dynamic holograms by nanosecond and picosecond laser pulses in solid-state fullerene-containing matrices

The results of a complex investigation of the recording of dynamic holograms by pulsed radiation with a duration of 20 ns and 300 ps in fullerene-containing media based on porous glasses and polymethyl methacrylate matrices are reported. Spectral analysis of these media in the range 300–700 nm was performed. The efficiency of hologram recording was found to relate with the occurrence of a band at 330 nm in the absorption spectrum of a medium. It is shown that dynamic holograms can be recorded in the fullerene-containing media by nanosecond and picosecond pulses. In the latter case, holograms arise mainly due to a change in the electronic polarizability of fullerene molecules, which is almost inertialess. The results obtained can be used in the development of ultrafast switching devices based on dynamic holograms.     

The use of commercial fine-grain films for computer-generated holograms

The possible use of commercial fine-grain films for computer-generated binary holograms is described. Three different types of film are used. Image quality improves with film resolution but if the resolving power is higher than a minimum value needed for the phase level resolution, the contrast (γ value) of the film has a pronounced effect on the quality of the image reconstructed optically from the hologram. The possible generation of binary holograms by computers with reduced central memory is also studied.     

利用傅里叶变换全息图实现彩色胶片存储

本文提出一种利用傅里叶变换全息图存储彩色胶片的方法.在参考光路和透明片后置入采栅,以红、绿、蓝三种波长记录+1级谱的点全息图.当三色光分别照明各自的全息图时,可再现两个真彩色图像.