We show, that by performing a simultaneous analysis of the angular dependencies of the +/- first and the zeroth diffraction orders of mixed holographic gratings, each of the relevant parameters can be obtained: the strength of the phase grating and the amplitude grating, respectively, as well as a potential phase between them. Experiments on a pure lithium niobate crystal are used to demonstrate the applicability of the analysis.
Microstructure of reflection holographic grating fabricated via a photo-isomerization process in an absorptive azopolymer film is analyzed. A surface relief formation takes place on the film surface even in the reflection holographic configuration. The polarization-dependent diffraction efficiency and the polarization analysis reveal that the polarization grating structure inside the film strongly depends on the amount of optical absorption experienced by the two writing beams. Theoretical analysis shows that the reflection polarization grating, while mimicking a cholesteric liquid crystal str…
We discuss the applicability of holographically recorded gratings in photopolymers and holographic polymer-dispersed liquid crystals as neutron optical elements. An experimental investigation of their properties for light and neutrons with different grating spacings and grating thicknesses is performed. The angular dependencies of the diffraction efficiencies for those gratings are interpreted in terms of a rigourous coupled wave analysis. Starting from the obtained results we work out the lines for the production of an optimised neutron optical diffraction grating, i.e., high diffraction effi…
The ring interferometer with zero optical path difference known as Sagnac one is offered with a diffraction splitting of the entering light beam. As the beamsplitter, a transmission holographic Bragg grating is used. Conditions of normal operation of this interferometer achieve under the equal intensity of beam copies and the adjustable phase shift between them in its two interferometer shoulders. These conditions are met with the holographic grating, which provides the phase shift 180^0 on the central Bragg wavelength. Experimental approbation of the modified interferometer validates the expe…
Measurement and analysis of diffraction parameters of thick transmission holographic phase gratings recorded on PHC-488 photopolymer are presented. Precision determination of the spatial grating period is executed by Bragg angle measurement for two precisely known wavelengths in the first diffraction order and also by Bragg angle measurement on one wavelength in the first and second diffraction orders. Determination of actual grating thickness and depths of spatial modulation of a holographic recording, which are responsible for their main optical characteristics, is carried out with the appli…
We performed light optical diffraction experiments on a nanoparticle-polymer volume holographic grating in an angular range including also far off-Bragg replay. A comparison of three diffraction theories - on the same level of complexity - with our experimental results shows that the dynamical theory of diffraction and the first-order two-wave coupling theory using the beta-value method fit the data very well. In contrast, the prevalent two-wave coupling theory using the K-vector closure method yields a poor fit with an order of magnitude worse mean squared error. These findings must be consid…
What we believe to be a new type of resonant coupling of an incident bulk wave into guided modes of a slab with a thick holographic grating is shown to occur in the presence of strong frequency detunings of the Bragg condition. This happens through the reflection of the strongly noneigen +1 diffracted order with the slab-grating boundaries, the resultant reflected waves forming a guided slab mode. Rigorous coupled-wave analysis is used for the numerical analysis of the predicted resonant effects. Possible applications include enhanced options for the design of multiplexing and demultiplexing s…
Standard multiple-beam holography has been largely used to produce gratings in polymer-liquid crystal composites, like POLICRYPS, H-PDLC gratings and POLIPHEM [1]. In this work we present a different approach to liquid crystalpolymeric grating production, based on the Computer-Generated Holography (CGH). The great advantage of using CGH is that interferometer-based schemes are no longer necessary, avoiding problems related to long term stability of the interference pattern and multi-beam complex optical setup. Moreover, the CGH technique allows a wider choice of pattern designs. In this prelim…
A polymer/liquid crystal-based fiber Bragg grating (PLC-FBG) is fabricated with visible two-beam holography by photo-induced modulation of a pre-polymer/LC solution infiltrated into the hollow channels of a solid core photonic crystal fiber (PCF). The fabrication process and effects related to the photonic bandgap guidance into the infiltrated PCF, and characterization of the PLC-FBG are discussed. Experimental data here presented, demonstrate that the liquid crystal inclusions of the PLC-FBG lead to high thermal and bending sensitivities. The microscopic behavior of the polymer/liquid crystal…
We discuss the applicability of holographically patterned polymers, polymer dispersed liquid crystals, and nanoparticle-polymer composites as optical elements for cold neutrons. Requirements concerning the spacing, thickness or strength of the grating for certain types of neutron optical elements, e.g., 2-port or 3-port beamsplitters, are discussed in the framework of a rigorous coupled-wave analysis. Finally, a roadmap to neutron mirrors, e.g., for interferometers, is drawn.
Holographic gratings with topological defects (branching of one or more fringes) are widely used for generating light beams with optical vortices (OV). This work presents an analysis of OV beams produced by binary computer-generated holograms enlightened by Gaussian beams centered at the fringe bifurcation point. Usually such beams are considered as analogs of the standard solutions of paraxial wave equation - Laguerre-Gaussian (LG) modes representing classical examples of OVs. However, the intensity profile and the whole process of their spatial evolution show important differences from the L…
We demonstrate the use of nanodiamond in constructing holographic nanoparticle-polymer composite transmission gratings with large saturated refractive index modulation amplitudes at both optical and slow-neutron wavelengths, resulting in efficient control of light and slow-neutron beams. Nanodiamond possesses a high refractive index at optical wavelengths and large coherent and small incoherent scattering cross sections with low absorption at slow-neutron wavelengths. We describe the synthesis of nanodiamond, the preparation of photopolymerizable nanodiamond-polymer composite films, the constr…
The preparation of neutron-optical phase gratings with light-optical holography is reviewed. We compare the relevant concepts of i) Kogelnik's theory for Bragg diffraction of light by thick volume gratings, which can be used to analyze holographic gratings with both light and neutrons, and ii) the dynamical theory of neutron diffraction. Without going into mathematical detail, we intend to illuminate their correspondence. The findings are illustrated by analyzing data obtained from reconstruction of nanoparticle holographic gratings with both light and neutrons.
We present a three-Charge-Coupled-Device (three-CCD) camera constructed upon multiplexed volume holographic gratings. Three incoherent gratings are written on the same holographic plate to guide the incident light into the three monochromatic channels, where images of red, green and blue light are recorded separately by CCD cameras. The reconstructed chromatic image from the monochromatic images shows superior qualities over the images taken by a single CCD camera.
A new method to generate and control the amplitude and phase distributions of a optical vortex beam is proposed. By introducing a holographic grating on top of the dielectric waveguide, the free space vortex beam and the in-plane guiding wave can be converted to each other. This microscale holographic grating is very robust against the variation of geometry parameters. The designed vortex beam generator can produce the target beam with a fidelity up to 0.93, and the working bandwidth is about 175 nm with the fidelity larger than 0.80. In addition, a multiple generator composed of two holograph…
A rigorous coupled-wave analysis of birefringent holographic gratings with periodically-modulated dielectric tensor along an in-plane direction and tensor variations in the thickness direction
A method to generate the optical vortex beam with arbitrary superposition of different orders of orbital angular momentum (OAM) on a photonic chip is proposed. The distributed Fourier holographic gratings are proposed to convert the propagating wave in waveguides to a vortex beam in the free space, and the components of different OAMs can be controlled by the amplitude and phases of on-chip incident light based on the principle of Fourier transformation. As an example, we studied a typical device composed of nine Fourier holographic gratings on fan-shaped waveguides. By scalar diffraction calc…
Laguerre-Gaussian (LG) beams are used in many research fields, such as microscopy, laser cavity modes and optical tweezing. We develop a holographic method of generating pure LG modes (amplitude and phase) with a binary amplitude-only Digital Micromirror Device (DMD), as an alternative to the commonly used phase-only Spatial Light Modulator. The advantages of such a DMD include very high frame rates, low cost and high damage thresholds. We show that the propagating shaped beams are self-similar and their phase fronts are of helical shape as demanded. We estimate the purity of the resultant bea…
We present a detailed experimental investigation on polarization-isotropic and polarization-anisotropic holographic scattering in lithium niobate crystal doped with iron when recording parasitic gratings with an ordinary polarized pump beam. The kinetics of both types of scattering during the whole process of recording is studied. Holographic scattering is presented as a simple technique to monitor the energy transfer between beams of different polarization. Moreover, the spectral and the angular dependence of the transmitted intensity of the crystal during the reconstruction of the auto-gener…
Prior to the invention of holography or lasers, Bragg's X-ray microscope opened the door to optical computation in short-wavelength studies using spatially coherent visible light, including phase retrieval methods. This optical approach lost ground to semiconductor detection and digital computing in the 1960s. Since then, visible optics including spatial light modulators (SLMs), array detectors and femtosecond lasers have become widely available, routinely allowing versatile and computer-interfaced imposition of optical phase, molecular coherent control, and detection. Today, high brilliance X…
Optical holography has undergone rapid development since its invention in 1948, but the accompanying speckles with randomly distributed intensity are still untamed now due to the fundamental difficulty of eliminating intrinsic fluctuations from irregular complex-field superposition. Despite spatial, temporal and spectral averages for speckle reduction, it is extremely challenging to reconstruct high-homogeneity, edge-sharp and shape-unlimited images via holography. Here we predict that holographic speckles can be removed by narrowing the probability density distribution of encoded phase to hom…
Traditional methods for generating orbital angular momentum (OAM) light include holographic diffraction gratings, vortex phase plate and spatial light modulator. In this article, we report a new method for high efficient OAM light generation. By pumping an external cavity contains a quasi phase matching nonlinear crystal with a fundamental OAM carrying light and properly aligning the cavity, mode matching between the pump light and the cavitys higher order Laguerre-Gaussian (LG) mode is achieved, conversion efficiency up to 10.3 percentage have been obtained. We have demonstrated that the cavi…
