共查询到20条相似文献,搜索用时 15 毫秒
1.
We have studied the anisotropic diffraction properties of the stratified volume holographic gratings recorded in photorefractive media using the anisotropic coupled wave theory. It is shown that the diffraction efficiency of such system exhibit the uniform periodic Bragg selectivity properties. In addition the dependence of the stratified volume holographic optical elements (SVHOEs) diffraction properties on the buffer-layer thickness, grating-layer thickness, number of modulation layers, and total thickness of system are discussed in detail. 相似文献
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We present a theoretical and experimental investigation of Bragg scattering of surface magnetostatic waves (SMSW) by a time-independent, spatially periodic magnetic field when the wave orientation is arbitrary with respect to the magnetization field. In the theoretical section the theory of single-mode Bragg diffraction is generalized to the case of waves with arbitrary dispersion propagating through an anisotropic medium. The calculated results are, on the whole, supported by experimental measurements on SMSW. We demonstrate that a geometry which in isotropic media leads to a sinusoidal distribution of diffraction order amplitudes as a function of penetration into the differing lattice, can lead to a nearly exponential distribution of such amplitudes in anisotropic media. The anisotropy of the interaction between SMSW and the magnetic diffracting lattice is manifested by anomalously high scattering efficiencies for certain cases of relative orientation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 76–85, November, 1988. 相似文献
4.
Xuefeng Yang Weibin Li Dao Hua Zhang 《Applied Physics A: Materials Science & Processing》2012,107(1):123-126
We present subwavelength periodic gratings achieved by employing a metallic grating waveguide heterostructure (MGWHS). The
mask can be designed to make one of its diffraction order (±mth) waves resonate with the surface plasmon wave supported by the MGWHS. With a finite-difference time-domain method, we numerically
demonstrate that one-dimensional periodic structure of about 60 nm feature, which is far beyond the diffraction limit, can
be patterned with the interference of the 3rd diffraction order waves of the mask at a wavelength of 546 nm. The technique
can also be extended to two-dimensional patterns using circularly polarized incidence and for the incidence with an angle
θ. 相似文献
5.
Methods for calculating the spectral properties of multilayer anisotropic structures are described. The structures comprise plane-parallel polarizing gratings made of linear conductors. The conductors in adjacent gratings are arbitrarily directed. The methods employ mathematical approaches used in the interference optics of multilayer isotropic structures. 相似文献
6.
The formalism of Rokushima and Yamakita [J. Opt. Soc. Am. 73 (1983) 901] treating the diffraction on planar multilayered 1D anisotropic gratings is extended to the diffraction on anisotropic 2D multilayer grating structures bi-periodic in the plane parallel to the interfaces. In addition to the oblique incidence of plane waves, the case of normal incidence is also treated. The goal of the paper is to provide a basis for the formal analysis of 2D patterned multilayers with natural or induced anisotropies. For example, such structures are of interest in the design of new magnetic and magneto-optic devices. In view of the fact that the anisotropies have often a negligible effect on the energy distribution among diffracted modes with respect to the isotropic case the optical response is alternatively expressed in terms of the ellipsometric parameters of diffracted waves. The present analysis represents generalization of the problem of electromagnetic wave interactions in planar multilayers consisting of layers characterized by a general permittivity tensor treated by Yeh [J. Opt. Soc. Am. 69 (1979) 742]. 相似文献
7.
Ci-bo LOU Li-qin TANG Dao-hong SONG Xiao-sheng WANG Jing-jun XU Zhi-gang CHEN 《Frontiers of Physics in China》2008,3(1):1-12
The study of wave propagation in periodic systems is at the frontiers of physics, from fluids to condensed matter physics,
and from photonic crystals to Bose-Einstein condensates. In optics, a typical example of periodic system is a closely-spaced
waveguide array, in which collective behavior of wave propagation exhibits many intriguing phenomena that have no counterpart
in homogeneous media. Even in a linear waveguide array, the diffraction property of a light beam changes due to evanescent
coupling between nearby waveguide sites, leading to normal and anomalous discrete diffraction. In a nonlinear waveguide array,
a balance between diffraction and self-action gives rise to novel localized states such as spatial “discrete solitons” in
the semi-infinite (or total-internal-reflection) gap or spatial “gap solitons” in the Bragg reflection gaps. Recently, in
a series of experiments, we have “fabricated” closely-spaced waveguide arrays (photonic lattices) by optical induction. Such
photonic structures have attracted great interest due to their novel physics, link to photonic crystals, as well as potential
applications in optical switching and navigation. In this review article, we present a brief overview on our experimental
demonstrations of a number of novel spatial soliton phenomena in light-induced photonic bandgap structures, including self-trapping
of fundamental discrete solitons and more sophisticated lattice gap solitons. Much of our work has direct impact on the study
of similar discrete phenomena in systems beyond optics, including sound waves, water waves, and matter waves (Bose-Einstein
condensates) propagating in periodic potentials.
相似文献
8.
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. 相似文献
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光轴方向任意时光折变晶体中体全息光栅的衍射性质 总被引:2,自引:2,他引:0
利用坐标旋转方法和Kogelnik耦合波理论,建立了光轴方向任意时单轴晶体中体光栅布拉格衍射的耦合波方程,分析了Li NbO3晶体的光轴方向对光折变体全息光栅的各向同性和各向异性布拉格衍射性质的影响。模拟计算表明,在给定光栅的结构参量时,通过适当选择光轴方向角可以使得光折变体光栅的各向同性和各向异性布拉格衍射的衍射效率达到最大,给出了相应类型的衍射效率取得最大值时晶体光轴的大致方向。这些理论分析为光折变体全息光学器件的优化设计和进一步广泛应用提供了很好的理论参考依据。 相似文献
11.
We generalize to magnetically isotropic but electrically anisotropic media the spinor formalism previously developed for isotropic media. 相似文献
12.
Efficient techniques to achieve isotropic edge enhancement in optics involve applying a radial Hilbert, Laguerre-Gaussian,
or differentiating filter on the object spectrum. We demonstrate a simple setup for isotropic edge-enhancement in soft-X-ray
microscopy, using a single Laguerre-Gaussian zone plate (LGZP). Since the LGZP acts as a beam-splitter, diffraction efficiency
problems usually associated with X-ray microscopy optics are not present in this system. As numerically demonstrated, the
setup can detect optical path differences as small as λ/50 with high contrast. 相似文献
13.
Francisco Javier Salgado-Remacha Francisco Jose Torcal-MillaLuis Miguel Sanchez-Brea Eusebio Bernabeu 《Optics and Lasers in Engineering》2011,49(3):356-360
Steel tape is used in optical applications due to its mechanical properties. However, roughness of steel surfaces affects to wave propagation. The effect can be observed using diffraction gratings with low periods. In such a case, self-images of the grating appear at certain periodic distances from the grating (Talbot planes). When standard steel is used, the contrast of Talbot self-images strongly decreases with the distance from the grating. In this work, we prove that controlling the surface quality of steel, it is possible to improve its optical behavior and, as a consequence, high quality surface steel represents a good choice for diffractive optics when the use of chrome-on-glass masks is not indicated. As an example, we have manufactured a diffraction grating over a high quality steel surface by means of an ablation process with a nanosecond pulsed laser. The contrast of the self-images for these gratings decreases very slowly with the distance, in comparison with the self-images obtained with standard steel tape gratings. 相似文献
14.
An analysis is made of acoustooptic Bragg diffraction in a paratellurite crystal in the case of a slow shear acoustic wave. It is shown that the isotropic acoustooptic interaction in crystals has characteristic physical features, which distinguish it from the well-known anisotropic interaction. The isotropic interaction under study is shown to be a more complicated process than diffraction in optically isotropic media. A theoretical and experimental study of the dependences of Bragg angle of incidence on the ultrasound frequency was made. Expressions for the calculation of this dependence are presented, which give results that agree well with the experimental data. The dependences of the isotropic-diffraction efficiency on the acoustic power were studied. For the first time, it was found that the corresponding dependences for anisotropic and isotropic interactions are substantially different. It is shown that the isotropic interaction under study is weaker than the anisotropic interaction. However, the isotropic-diffraction efficiency has a noticeable value and can reach tens of a percent. 相似文献
15.
LOU Ci-bo TANG Li-qin SONG Dao-hong WANG Xiao-sheng XU Jing-jun CHEN Zhi-gang 《Frontiers of Physics》2008,3(1):1
The study of wave propagation in periodic systems is at the frontiers of physics, from fluids to condensed matter physics, and from photonic crystals to Bose-Einstein condensates. In optics, a typical example of periodic system is a closely-spaced waveguide array, in which collective behavior of wave propagation exhibits many intriguing phenomena that have no counterpart in homogeneous media. Even in a linear waveguide array, the diffraction property of a light beam changes due to evanescent coupling between nearby waveguide sites, leading to normal and anomalous discrete diffraction. In a nonlinear waveguide array, a balance between diffraction and self-action gives rise to novel localized states such as spatial “discrete solitons” in the semi-infinite (or total-internal-reflection) gap or spatial “gap solitons” in the Bragg reflection gaps. Recently, in a series of experiments, we have “fabricated” closely-spaced waveguide arrays (photonic lattices) by optical induction. Such photonic structures have attracted great interest due to their novel physics, link to photonic crystals, as well as potential applications in optical switching and navigation. In this review article, we present a brief overview on our experimental demonstrations of a number of novel spatial soliton phenomena in light-induced photonic bandgap structures, including self-trapping of fundamental discrete solitons and more sophisticated lattice gap solitons. Much of our work has direct impact on the study of similar discrete phenomena in systems beyond optics, including sound waves, water waves, and matter waves (Bose-Einstein condensates) propagating in periodic potentials. 相似文献
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In the current communication, the problem of plane wave diffraction by a conductible plate of finite length in the presence of cold plasma is investigated. The boundary-value problem corresponding to this model is formulated by Fourier transform which then leads to the Wiener?Hopf equation. The resulting equation has been solved by the Wiener?Hopf procedure in a standard way. The separated field (diffracted field) is analyzed in an anisotropic medium using asymptotic expansion and modified stationary phase method. The problem can be made simple by assuming ε2→0, where ε2 is the element of permittivity tensor. This happens, if the operating frequency is assumed to be very large as compared to ωc (cyclotron frequency) while it is of same order of ωp (the plasma frequency). The case ε1 =1, ε2→0 leads to the results for soft plate of finite length in an isotropic medium. Graphical study is performed to investigate the behavior of separated field for various physical parameters for isotropic and anisotropic media. 相似文献
18.
We show that, in low-dimensional photonic bandgaps, wave diffraction resulting from localization in the translational-invariant directions is strongly influenced by the photonic band structure of the periodic crystal, leading to new kinds of wave localization. In particular, for a periodic layered structure we show that, close to a bandgap edge, diffraction is enhanced, with a transition from a parabolic diffraction curve-typical of isotropic media and supporting Gaussian beams-to hyperbolic or elliptic diffraction curves. In the last two cases localization in the form of stationary X-shaped or sinc-shaped waves is possible. 相似文献
19.
The coupled wave theory of Raman and Nath diffraction is extended to the case of thin anisotropic holographic media with grating
vector parallel to the medium boundaries. Solutions for the wave amplitudes, diffraction efficiencies, and angular mismatch
sensitivities are given in transmission geometries for the case of mixed dielectric and absorption modulations. For an apparent
distinction, the results are given only for dielectric modulation. The main difference of the new results, with respect to
the expressions valid for isotropic media, arises due to the walk-off between the wave-front and energy propagation directions.
The difference is particularly important in materials with large birefringence, such as organic crystals, ordered polymers,
and liquid crystalline cells. 相似文献
20.
We realize a unidirectional transmission by cascading two nonparallel gratings (NPGs) made of isotropic, lossless, and linear media. For a pair of orthogonal linear polarizations, one of the gratings is designed as a polarizer, which is a reflector for one polarization and a transmitter for the other; another grating is designed as a polarization converter, which converts most of one polarized incident wave into another polarized transmitted wave. It is demonstrated by numerical calculation that more than 85% of the incident light energy can be transmitted with less than 1% transmission in the opposite direction for linearly polarized light at normal incidence, and the relative bandwidth of the unidirectional transmission is nearly 9%. The maximum transmission contrast ratio between the two directions is 62 dB. Unlike one-way diffraction grating, the transmitted light of the NPGs is collinear with the incident light, but their polarizations are orthogonal. 相似文献