A holographic wavefront sensor based on a spatial light modulator (SLM) for displaying computer-generated holograms (CGH) is a flexible and simple method for analyzing the wavefront. This article discusses an algorithm for the synthesis of holographic structures based on a blazed diffraction grating (Echelette grating). As a result of the reconstruction of such CGHs the light diffracts predominantly into one diffraction maximum. The experiments carried out confirm the effectiveness of the proposed algorithm when measuring the wavefront described by one or several Zernike polynomials simultaneously.
Laser radiation for a high precision measurement such as nanostructure measurement needed to be clean of wavefront aberrations. However, only expensive lasers with stabilization can achieve such robust parameters. The emission is needed to be corrected via adaptive optics. Nevertheless, high precision measurement of wavefront aberrations is necessary to high precision correction. The present work is dedicated to the problem of computer-generated Fourier holograms application for measurement of optical wavefront curvature with high precision. Mathematical modeling and experimental results of the method with the comparison of different approaches are presented.
Currently rainbow and volume holograms are the most used protective holograms. The production technology of such holograms allows to replicate them at the industrial level without deteriorating their protective properties. However, new methods of obtaining protective holograms have been recently studied. Previously has been repeatedly demonstrated the possibility of applying computer-generated Fourier holograms (CGHs) to scattering, non-photosensitive media. We want to study the possibilities of obtaining Fourier holograms on such media and discover protective properties of such holograms. We consider the possibility to obtain binary and halftone CGHs on various mediums in mass-production, including metallized films, self-adhesive labels on paper basis, paper and laser film. For the application we used technologies of thermal transfer and laser printing, as well as direct laser recording. The reconstruction was carried out both optically and using a smartphone. This paper presents experiments and results of mass-production holograms on the selected mediums. We have simulated the distortions that may occur after manufacturing of CGHs, analyzed the quality of the image being reconstructed under various application methods. We show that such holograms can be used as security elements in specific cases. Still, there are the possibilities of improving the quality of deposition of protective hologram elements depending on the used technology, as well as the possibility of taking into account potential distortions during the synthesis of holograms.
Currently, diffractive optical elements with light guide substrates are used in miniature display systems especially in systems for vehicles, aircraft, and systems, where the observed image overlaps with the real scene. It is possible to get rid of the double image and zero order (this feature is inherent in computer generated hologram Fourier) as a result of synthesis of complex Fresnel hologram. As a result, we can synthesize a complex hologram that is free of the twin image and the zero-order light using a single spatial light modulator. The holograms are recorded with a spatial light modulator in a projection mode. This configuration consists of glass substrate with computer generated holograms Fresnel and diffraction gratings, as a diffractive optical element, for input and output of radiation. Reconstructing beam is incident on the computer generated holograms Fresnel, and then through diffraction grating 1 radiation is introduced into the plate at an angle of TIR and spread in it. When the light reaches the surface of the substrate with a diffraction grating 2, part of the light emerges from it. diffraction gratings are two diffraction gratings, which should have different diffraction to ensure uniform brightness of the observed image. It should be noted that to ensure the non-uniform diffraction efficiency of diffraction grating exit area was divided into multiple zones. Thus, the zonal diffraction grating was recorded with its exposure value. Light beams diffracted on computer generated holograms Fresnel enter and then multiple output from substrate, thus forming for observer an increased image of the test object.
In this paper, we used an algorithm for the synthesis of binary computer generated holograms Fourier, applying pseudo-random phase masks to increase the intensity of high-frequency components of holograms. A feature of such a computer generated hologram is that the generated symbolic information is an axis-symmetrical picture, which is determined by the mathematical description of the Fourier transformation. The holograms are recorded in a collimated beam with the help of a spatial light modulator in a projection mode. The hologram is recorded with a decrease in linear dimensions to reduce the distortions introduced by spatial light modulator. The progress of computer-synthesized holograms has fallen on the progress of computer technology. In this article, the key issue is the photochemical procedure of processing holograms after their exposure. This processing allows to increase the transmittance of the hologram up to 96%, which enables to install computer generated holograms directly in the field of view of a person. A positive effect of the photochemical treatment process is also an increase in the overall diffraction efficiency of the hologram and redistribution of the intensity from the central point (radiation that did not diffract on the structure and passed through the hologram) to the image that was formed as a result of diffraction of radiation.
Optical position encoders working according to the interference method consists of a measurement scale and a measuring head moving along each other. The scale has a reflection diffraction grating on its surface and the measuring head has a transmission diffraction grating with same period inside. Laser light passing and diffracting through these two gratings creates an interference signal on an optical detector. Decoding of the interference signal phase allows to determinate current position. Known optical position encoders use complex optical schemes and some phase optical elements to form several quadrature signals with different phase for higher encoder accuracy. Previously we researched such kind of schemes [1, 2]. In this paper we propose to use a common optical scheme without phase elements but with a complex structured measuring head grating for this purpose to simplify an optical scheme and alignment requirements. The optical scheme of position encoder based on measuring head grating with specific structure is research and described in this paper.
In this paper, we describe and analyze the distortions that occur in the production of Fourier holograms by the projection method using SLM and in a printed way. Mathematical simulation of projection method allowed to take into account the influence of diffraction on apertures on the structure of the obtained hologram. It is shown that the final structure after recording and the simulation result are similar. When analyzing the printed method of obtaining holograms, we took into account the distortions that arise due to incorrect consideration of the resolution of the printer and the wrong choice of the size of the printed hologram Numerical results of simulation and holograms reconstruction are obtained.
Optical position encoders working according to the interference method consists of a measurement scale and a measuring head moving along each other. The scale has a reflection diffraction grating on its surface and the measuring head has a transmission diffraction grating with same period inside. Laser light passing and diffracting through these two gratings creates an interference signal on an optical detector. Decoding of the interference signal phase allows to determinate current position. Known optical position encoders use complex optical schemes and some phase optical elements to form several quadrature signals with different phase for higher encoder accuracy. Previously we researched such kind of schemes [1, 2]. In this paper we propose to use a common optical scheme without phase elements but with a complex structured measuring head grating for this purpose to simplify an optical scheme and alignment requirements. The optical scheme of position encoder based on measuring head grating with specific structure is research and described in this paper.
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