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...     

Formation of holographic transmission and reflecting gratings in photopolymers under light-induced absorption

The formation of holographic transmission and reflection gratings is examined taking into consideration photoinduced absorption in photopolymer materials. The holographic gratings are assumed to be formed by light beams with arbitrary amplitude profiles. The problem is solved analytically in the zero-and first-harmonic approximation of the monomer concentration and refractive index with allowance for the interference-pattern contrast, an arbitrary degree of photopolymerization nonlinearity, and the dependence of the diffusion coefficient on the degree of polymerization. The effect of beam-amplitude profiles and light-induced absorption on the spatial profiles of holographic gratings is studied using numerical simulation. The effect of light-induced absorption on the diffraction characteristics of holographic gratings is discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 81–89, October, 2006.     

Holographic grating based Ebert spectrograph

In this paper we discuss the aberration properties and design procedure of in-plane Ebert spectrograph using conventional as well as holographic diffraction gratings. In both cases the gratings are situated at the well-known √3-position so that the spectrum can be recorded on a flat surface. It has been found that the holographic grating system has better resolution than the conventional grating system. The design parameters of a medium sized holographic grating spectrograph in which a concave spherical mirror is mounted in the off-axis configuration have been specified. The performance of the spectrograph has been evaluated by plotting spot diagram.     

Holographic formation of dynamic transmission diffraction gratings in a photopolymer material in the process of two-beam interaction at low contrasts

In the present study, the process of formation of holographic transmission diffraction gratings in photopolymer media is investigated at low contrasts with allowance for self-diffraction of recording waves. A theoretical model for the first spatial harmonics of the refractive index grating is constructed based on a solution of the coupled kinetic photopolymerization and diffraction equations. The temporal dynamics of amplitude and phase spatial profiles of harmonics, diffraction efficiency, and angular selectivity of recorded gratings is theoretically investigated. The calculated and experimental data are compared. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 35–42, November, 2006.     

金纳米颗粒掺杂光致聚合物的体全息混合光栅模型

金纳米颗粒掺杂光致聚合物在全息曝光过程中,光产物周期分布会形成折射率调制相位型主光栅,同时金纳米颗粒周期分布形成由局域表面等离子体共振引起强吸收的振幅型辅助光栅。研究基于耦合波理论的一种混合光栅模型,分析了光栅的体全息光学特性。结果表明,混合光栅中的折射率光栅和吸收光栅都能够提升体光栅的衍射效率; 体光栅的角度选择性也可以得到明显的改善。     

Optical properties of sliced multilayer gratings

Fabrication, calculation and optical properties of gratings fabricated by bevel cutting multilayer structures are discussed. Such gratings have very short period (about 100 nm) and provide high angular dispersion as compared to ruled, holographic or multilayer coated gratings without reduction of diffraction efficiency. Using graded multilayers it is possible to produce sliced multilayer gratings (SMG) with graded period (GSMG), which can focus radiation in one direction. Examples of SMG for various wavelengths in the interval 2–20 nm are considered.     

Nonlinear Model of Record and Readout of Holographic Transmission Diffraction Gratings in Absorbent Photopolymers. Part I. Theoretical Analysis

In the present study, record and readout of holographic transmission diffraction gratings in photopolymer media are investigated with allowance for an arbitrary degree of nonlinearity of photopolymerization, contrast of interference patterns, and absorption and arbitrary relative contributions of polymerization and diffusion recording mechanisms. A theoretical model of (N + 1) 3-D harmonics of the refractive index grating, based on a solution of the coupled kinetic photopolymerization equations, allows the time dynamics of harmonic amplitudes, 3-D refractive index profile, diffraction efficiency, and angular selectivity of the recorded gratings to be investigated. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 56–63, May, 2005.     

Study of angular responses of mixed amplitude--phase holographic gratings: shifted Borrmann effect

We present theoretical results for angular responses of transmitted and diffracted beams in mixed amplitude-phase holographic gratings. Experimental results for gratings recorded in photographic emulsions and developed without a bleaching bath, with diffraction efficiencies of >20% , are also presented. The model shows an angular shift between minimum transmittance and maximum diffraction efficiency when both index modulation and absorption coefficient modulation are present. Also, the Borrmann effect was found outside the Bragg angle. This method can be extended to a study of the mechanism of image formation in materials such as bacteriorhodopsin and azo-dye-doped polymers that exhibit both types of modulations (index and absorption).     

Quasi-Fourier transform hologram format for data storage

For a recording medium such as dichromated gelatin, a quasi-Fourier transform holographic memory is preferred over the exact Fourier transform. We proceed here with angular multiplexing and consider undesired reconstructed waves such as cross-talk noise, and show that the signal-to-noise ratio is 33 dB for 20 angular multiplexed elements in 25 μm thickness of the recording medium. We also study the energy coupling between gratings to standardize the diffraction efficiency of each multiplexed grating.     

Peculiarities of spontaneous grating generation in light-sensitive waveguide layers during holographic grating formation

The generation of spontaneous (noise) gratings during the simultaneous formation of a holographic grating in thin (on the order of the cutoff thickness of the TE₀ waveguide mode) AgCl-Ag films by two laser beams with λ = 532 nm and polarization vectors that make an angle of 45° with the plane of incidence have been studied. The electron microscopy images and diffraction patterns have revealed a significant difference of the spontaneous-grating structure from the structure obtained under irradiation by one laser beam. The spontaneous gratings have a significant spread in the directions of their wave vector, and the diffraction pattern (recorded using a probe beam with λ = 337 nm) has the form of a bundle of diverging arcs that intersect at one point. This difference is caused by self-diffraction from the holographic grating, which is responsible for the main diffraction peaks with odd orders, the growth of spontaneous gratings because of the interference of the beams diffracted by the holographic grating with the waveguide TE₀ modes scattered in the film, and silver transport to the interference minima. The diffraction patterns are quantitatively analyzed and the period of the new (formed under two-beam irradiation) spontaneous gratings is calculated. The calculation results are in good agreement with the experimental data.     

Laser-induced fluorescence imaging of subsurface tissue structures with a volume holographic spatial-spectral imaging system

A three-dimensional imaging system incorporating multiplexed holographic gratings to visualize fluorescence tissue structures is presented. Holographic gratings formed in volume recording materials such as a phenanthrenquinone poly(methyl methacrylate) photopolymer have narrowband angular and spectral transmittance filtering properties that enable obtaining spatial-spectral information within an object. We demonstrate this imaging system's ability to obtain multiple depth-resolved fluorescence images simultaneously.     

Optical mosaic gratings made by consecutive, phase-interlocked, holographic exposures using diffraction from latent fringes

We propose and demonstrate a method for fabricating large optical mosaic gratings, i.e., gratings made by consecutive, phase-interlocked, holographic exposures on single substrates. It takes advantage of the latent fringes generated by the preceding exposure to align the substrate for the following exposure. Good angular alignment accuracy and period consistency between the fringes recorded by consecutive exposures can be achieved by using the large-area moiré pattern produced by the latent fringes and the alignment beams. Phase-interlocking accuracy of less than 4 degrees between consecutive exposures was experimentally achieved by using the heterodyne detection technique.     

High performance holographic polymer dispersed liquid crystal systems using multi-functional acrylates and siloxane-containing epoxides as matrix components

High performance transmission holographic polymer dispersed liquid crystals were fabricated using a mixture of radically photopolymerizable multifunctional acrylates and ring-opening photopolymerizable epoxides as monomers for matrix components with Nd:YAG laser (λ=532 nm). Functionality of multifunctional acrylates and concentration of LC were varied to optimize the performance of holographic gratings. Gratings with much higher diffraction efficiency (83% or 67%, respectively) were obtained from recording solution composed of dipentaerythritol penta/hexaacrylate,1vinyl2pyrrolidone, commercial liquid crystal E7, and 1,3-bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane with glycidyl function linked with disiloxane, or 1,3-bis[2-(1,2-epoxycyclohex-4-yl)ethyl]-1,1,3,3-tetramethyldisiloxane with cyclohexene oxide function and the same siloxane spacer (45:9:10:36), compared with the ordinary recording solution composed of dipentaerythritol penta/hexaacrylate, 1vinyl2pyrrolidone and E7 (<2%). The recording solution composed of 1,5-bis(3-glycidoxypropyl)-1,1,3,3,5,5-hexamethyltrisiloxane and 1,5-bis[2-(1,2-epoxycyclohex-4-yl)ethyl]-1,1,3,3,5,5-hexamethyltrisiloxane with trisiloxane spacer gave further improved diffraction efficiency (97% and 75%, respectively). Recording solutions contain trisiloxane derivatives gave gratings with considerably or moderately reduced angular deviation (0.83, 0.66 degree for trisiloxane derivatives from 1.2, 0.7 degree for disiloxane derivatives, respectively, for signal beam, and 0.76, 0.70 degree from 1.1, 1.0 degree, respectively, for the reference beam at 32 degree of external incident angle) from Bragg profile, namely 5.2 and 4.5% volume shrinkage for trisiloxane derivatives, and 7.5, 5.6% volume shrinkage for disiloxane derivatives, respectively. High diffraction efficiency over 95% with angular selectivity of 4.0 degree was obtained for the gratings formed from 1,5-bis[2-(1,2-epoxycyclohex-4-yl)ethyl]-1,1,3,3,5,5-hexamethyltrisiloxane when the concentration of E7 was reduced to 5%. Clearly phase-separated liquid crystal domains were observed by scanning electron microscopy. Grating spacing (about 900 nm) was close to the calculated value (965 nm) by Bragg equation. PACS 42.40.Eq     

Technique for characterization of dimensional changes in slanted holographic gratings by monitoring the angular selectivity profile

A method has been developed for retrieving the complete angular selectivity profile of transmission holographic gratings in one step. The method is applied to study in real time the shrinkage and changes in the effective optical thickness of a slanted holographic grating recorded in an acrylamide-based photopolymer. It can form the basis of a holographic sensor of analytes that cause a thickness change in the holographic medium. It can also be useful for the study and optimization of holographic recording materials and for quality control during production of holographic optical elements.     

Study on measuring refractive index modulation of volume phase holographic gratings

In this paper, we present an approach to measure the refractive index modulation of volume phase holographic gratings (VPHG) by use of its angular selectivity, with the advantage of avoiding the diffraction efficiency errors induced by noise. Based on Kogelnik's coupled wave theory for volume holographic gratings, the wave vectors matching relationship for reflective VPHG at different readout wavelengths is deduced and the diffraction efficiency as a function of readout angle is also obtained. Then an all-fiber experimental system is designed to measure corresponding diffraction efficiency with different readout angles for VPHG recorded in dichromate gelatin. By seeking the Bragg angle where diffraction efficiency is maximum and the blank angle where diffraction efficiency drops to the minimum value, the refractive index modulation can be calculated. The experiment results proves the feasibility of the method.     

Inscription of holographic gratings using circularly polarized light: influence of the optical set-up on the birefringence and surface relief grating properties

The polarization properties of the optical set-up used for holographic recording of diffraction gratings on azopolymer thin films are analyzed. The state of polarization of circularly polarized light is fully analyzed after reflection on a mirror at various incidences (Lloyd-mirror set-up). The Stokes analysis is performed using a photopolarimeter and the phase shift, the ellipticity and the azimuth orientation are compared with those calculated from Fresnel formulae. At large angles of incidence, an initially right circularly polarized (RCP) beam becomes elliptically polarized with an azimuth of nearly +45°. From these results, holographic diffraction gratings are recorded on an azobenzene-containing polymer thin film using (i) co- and contra-circularly polarized beams and (ii) a right circularly polarized beam interfering with a +45° linearly polarized light beam. Using Jones-matrix formalism, the polarization states of the diffracted orders from the birefringence (Δn) and the surface-relief (2Δd) gratings are derived and compared with experimental measurements. Finally, the induced local birefringences and surface-relief amplitudes are discussed in connection with atomic force microscopy measurements. The diffraction efficiencies obtained under the (+45°+RCP) and (LCP + RCP) (where LCP = left circularly polarized) configurations are thus compared and discussed. Received: 5 October 2001 / Revised version: 26 November 2001 / Published online: 17 January 2002     

Charging of glassy chalcogenide semiconductors in corona discharge and its effect on holographic grating formation

Recording of optical holographic gratings based on photostructural transformations in thin (≈ 1 μm) As₂S₃ and As₂S₃ semiconductor layers in the presence and absence of a corona discharge and also chemical etching of these gratings are studied. Initiation of a corona at the stage of interference grating recording is shown to improve the exposure contrast of metal-glassy chalcogenide semiconductor thin-film structures. The holographic sensitivity, diffraction efficiency, dynamic range, and contrast are also improved severalfold. When phase relief gratings formed in these layers are selectively etched in a chemical etchant in the presence of a corona, their profile becomes more regular and deeper by 25–30% and the diffraction efficiency increases by 30–50%.     

Activation Energy of Proton Migration in Mn- and Fe-Doped Lithium Niobate Obtained by Holographic Methods

The activation energy of thermal fixing of photorefractive gratings is determined in congruent and nearly stoichiometric lithium niobate crystals, both doped with iron or manganese. The novel technique called holographic scattering method is compared with the standard two-wave mixing method. A measurement of the angular distribution of the self scattered intensity and its possible analytical function is presented. The mathematical problems of the holographic scattering method are discussed applying the angular distribution functions.     

Holographic volume gratings in a glass-like polymer material

We demonstrate a possibility to write efficient and thermally stable volume holographic gratings in a glassy polymer material based on PMMA and phenanthrenequinone with layers prepared, by casting the liquid solution of ingredients on a substrate and drying to a solid state. A high concentration of phenanthrenequinone (up to 4 mol. %) makes it possible to use photosensitive layers of lower thicknesses (50–180 μm) for the recording of efficient holographic gratings. The exposing is followed by a thermal amplification of the grating due to diffusion of residual phenanthrenequinone molecules and fixation by an incoherent optical illumination. We present experimental temporal curves of the refractive index modulation and diffraction efficiency both under the exposure and the heating process. The behavior of the gratings under temperatures up to 140 °C has been studied. PACS 42.40.Eq; 42.70.Jk; 42.70.Ln