Littérature scientifique sur le sujet « Hologram inversion »

An encryption system that combines compressive sensing (CS) and two-step parallel phase shifting digital holography (PPSDH) using double random phase encoding (DRPE) is presented in this paper. The two-step PPSDH is a linear inline holographic scheme and is much suitable for encrypting the 2D/3D information in a single exposure. The distribution of random phase mask (RPM) in the DRPE is implemented using circular harmonic key which increases the security of the encryption process. In this system, the keys used to encrypt are spatial positions of the planes, wavelength, and rotation of the circular harmonics in RPMs, and CS acts as an additional key that makes the system more secure than the conventional optical encryption methods. At the transmission end, two-step PPSDH is applied to encrypt the object information in single hologram. The digital mirror device (DMD) is placed between the object and a single-pixel detector for acquiring fewer hologram measurements. At the receiver end, the single digital hologram is numerically recovered by using a CS optimization problem. The original complex object field is decrypted from the CS recovered holograms by the inversion of two-step PPSDH process with the help of the correct keys. The numerical simulations are presented for complex 2D and 3D objects to test the feasibility of the proposed encryption and decryption system. The proposed method carried out intensity and phase reconstruction of the original object field using single-pixel compressive imaging. The computer simulation results demonstrated that the encrypted information is highly secured with the rotation of the circular harmonic key. The sensitivity of the decrypted intensity and phase images is also studied with variations of the encrypted keys. The obtained results show that the proposed encryption scheme is feasible and has better security performance and robustness.

The object of research is optical-electronic methods and related digital information processing. One of the most problematic areas is the reconstruction of missing parts of the stored data and the inability to detect minor changes in the stored samples, as well as the reconstruction of the entire corrected template from its incomplete version. As part of the study, a correlation-optical approach to the problem of holographic associative memory was used, which made it possible to achieve highly efficient heteroassociative reconstruction of the entire corrected template from its incomplete version. The analysis of hologram models with phantom images and nonlinearly recorded holograms read in the associative mode shows a wide range of useful possibilities. It is primed not only in the tasks of reconstruction of data, but also in the case of insignificant changes in savings, highly effective heteroassociative reconstruction based on a non-interference mechanism. The analysis of the results of the correlation-optical approach to the problem of holographic associative memory shows that the described method opens up additional opportunities for solving the problems of detecting small changes in the object scene, which is important, in particular, for early registration of events and phenomena. It is related to the fact that the detection and localization of changes is carried out according to the difference in intensity across the image field (the effect of brightness inversion in the phantom image of referenceless hologram): the brightness of the image of the changed area is higher, and to a greater extent, the smaller the changes compared to the reference image. It should be especially noted that the specified properties of the nonlinear-holographic associative memory are realized not algorithmically, but physically, taking into account the fundamental nonlinearity of all natural processes, which is neglected when conducting a superficial (in the first approximation) analysis. Physical modeling of associative memory based on second-order holograms does not involve any circuit complications compared to the standard holographic procedure.

We have investigated the photoelectron diffraction (PED) from a SrF 2 epitaxial thin film on Ge(111) from the viewpoint of holographic inversion for imaging the atomic structure. The holographic interference fringes were retrieved from the PED pattern including a wide variety of diffraction features via averaging the pattern around each forward-scattering peak. Furthermore, another method for enhancing holographic fringes by subtracting one photoelectron hologram from another at slightly different kinetic energies was theoretically investigated.

At low temperatures many adsorbates arrange in lattice gas disorder on crystalline substrates. In a low energy electron diffraction (LEED) experiment this leads to diffuse intensities super-imposed on the sharp spots caused by the substrate. For the disordered adsorption system Ni(001)/K, we present two-dimensional intensity distributions as function of the electron energy and angle of incidence. They can be measured very fast (20 s per frame) and reliably using an automatic video based data acquisition technique. We show that diffuse intensity spectra DI(E) taken as function of energy for fixed surface parallel electron momentum transfer carry the information about the local adsorption structure. This is equivalent to conventional I(E) spectra taken for sharp spots. In the light of recent proposals it is shown that the diffuse single energy intensity pattern is not a hologram of the local structure because e.g. the reference wave is ill defined. However, the diffraction processes disturbing the pure reference wave cancel when the intensities of different energies are suitably averaged. It is demonstrated that the holographic reconstruction of real space information from such scanned energy data leads to reliable and well resolved atomic images. Full widths at half-maximum of such atomic images are not greater than 1 Å. Substrate atoms behind the reference atom in direction of the incident beam are imaged best. So, image reconstructions for different beam directions produce a full and high quality three-dimensional image of the local adsorption structure.

Textual semantics is studied on the basis of subjective — objective reciprocal feedback, where the objective field is reconstructed from the eidetic images with the inversion of their inner relations. The priority belongs to the textual inner world, and the objective field is determined with an epoch's concrete historical conditions. Mereology is developed within the framework of phenomenology as the logical theory dealing with the relation of "part –whole" that in difference to hermeneutics is based on the irreducibility of the whole to the parts and the reciprocity of this relation. The parts are divided into the autonomous and dependent, inner and outer ones. A text is regarded as a hologram where each part represents its functions within the whole. It is the textual frameworks that play the decisive role in textual integration together with reciprocal references of the distant parts and complementary relations. The paragon of framework is to be found in the cues of a role of a dramatic persona. It is due to distanced relations that the dimensionality of a text grows, it surpasses linear and planar limits, its depth and volume are revealed. Such means of frameworks as anaphora procure the textual division onto closed cycles.

Our contribution in this work is to detect, localize and quantify the noise sources radiated by a spur gear transmission mechanism. The imaging technique is used; it is based on the acoustic inverse frequency response function (IFRF). The IFRF is based on the inversion of the transfer matrix built between the source points represented by their complex source strengths and listening points represented by the complex pressures measured by the hologram. The measurements were performed in a semi-anechoic room where the floor is concrete and the walls are covered with glass wool. The complex acoustic pressures are measured by an antenna with microphones regularly spaced; it is placed above the noisy mechanism. The reconstruction problem is therefore an inverse problem and is said ill-posed; thus, regularizations are needed to stabilize and to find the best solutions. As regularization technique, the Tikhonov method is applied and the regularization parameters are chosen according to the L-curve method. The goal is to reconstruct as accurately as possible the acoustic field radiated by the transmission mechanism on a fictive and tangent plane to the noisy mechanism considered open and sometimes closed. The results obtained showed that the sources were located with good approximation. The IFRF method is able to reconstruct the sound sources responsible for the noise radiated by the mechanism without any a priori information of the sources distribution, and the visualization of spatial acoustic fields facilitate the understanding of the complex phenomena of radiation.

We examine the differences between low-energy electron-diffraction patterns (holograms) and optical holograms. We show that electron-diffraction patterns in solids are not analogous to optical holograms because of strong dynamical factors. We also show that low-energy electron holograms can be inverted by a large-wave-number small-angle integral transformation. The grid sizes in wave number and angular spaces used in the transformation are derived.

Nonlinear refraction in a new polymer material based on diglycidylether of bisphenol-A and containing 4-aminoazobenzene covalently attached to the polymer chains have been studied. The material was shown to exhibit fast nonlinear response (relaxation time about 20 ns, χ(3)= 5 × 10- 8 esu) together with slow one (relaxation time of the order of tens of hours). This makes it possible to record fast and long life (quasi stationary) phase holograms. An analysis of possible mechanisms for the refractive index nonlinear behavior in the new structure is presented. In particular, a role of electronic, thermal, orientation, and isomerization processes is discussed. It was for the first time shown that the rotational and inversion mechanisms of the cis → trans isomerization of the azo-compounds have determinative effect upon kinetics of the nonlinear refractive index relaxation. For the rotational mechanism the relaxation time was found to be 10-4 s meanwhile for the inversion mechanism it was 105 s.

Certain photochromic materials exhibit at liquid-helium temperature a special property of very high selectivity in frequency dimension. This phenomenon, commonly known as spectral hole burning (SHB), makes it possible to extend conventional spatial-domain optical data storage into the dimensions of frequency and time. We have applied SHB for ultrafast recording of holograms and coherent optical processing on the timescale of 10-12–10-13 s. To achieve ultrafast performance in the time domain, we use special organic dye-doped polymer materials, which provide SHB recording in a broad optical band width of 5–10 THz. In this paper, we discuss recording and playback of holograms of pico- and femtosecond time-and-space-domain signals using dye-doped SHB polymers at liquid-helium temperature. We discuss unusual properties of SHB holograms such as causality-related asymmetry of diffraction and inversion of the time coordinate, ultrafast frequency-domain processing, and associative recall of events.

Per mezzo del finanziamento ottenuto con il progetto North Atlantic Treaty Organization, Science for Peace and Security (NATO SPS) G-5014 è stata sviluppata una piattaforma robotica multi-sensore in grado di individuare oggetti sepolti plastici e metallici e generare dati per la successiva classificazione degli ordigni attraverso l’analisi di operatori specializzati. Utilizzare una piattaforma robotica permette di aumentare la sicurezza per gli operatori, perché completamente controllabile in remoto tramite un’interfaccia software web e permette di utilizzare diversi sensori per massimizzare la probabilità di rivelazione delle mine, mantenendo minima la probabilità di ricevere falsi allarmi. I sensori principali installati sono due RADAR operanti nello spettro delle microonde ( ≃2 GHz): un UWB Ground Penetrating RADAR (GPR), sviluppato appositamente per rilevare la posizione dell’oggetto sepolto all’interno dell’area illuminata, capace di rilevare oggetti sepolti durante il moto della piattaforma e un Holographic Subsurface RADAR (HSR), operante ad onda continua e singola frequenza, in grado di generare immagini olografiche che permettono di osservare la forma e le dimensioni degli oggetti sepolti nei primi 15 - 20 cm del sottosuolo e, tramite l’elaborazione con algoritmi di inversione del campo elettromegnetico, permette di ricostruire la scena tridimensionale che si trova di fronte all’apertura sintetica del RADAR. Le immagini che genera questo dispositivo consentono di discriminare gli ordigni da altri oggetti riflettenti le microonde ma del tutto inoffensivi (clutter). Il HSR progettato nel corso del progetto NATO SPS G-5014 costituisce un primo prototipo che soddisfava i requisiti richiesti dal progetto. Il frutto di questo lavoro ha riscosso interesse nella comunità scentifica e presso NATO SPS, generando un seguito: il progetto NATO SPS G-5731, tutt’ora in corso. Nell’ambito di quest’ultimo progetto si colloca il mio lavoro: ho contribuito allo sviluppo di un sistema RADAR per immagini a microonde in grado di migliorare, in termini di qualità di immagini prodotte (incrementando il rapporto segnale-rumore e la risoluzione) e di profondità di penetrazione (studiando le caratteristiche elettromagnetiche del suolo di interesse), le prestazioni del HSR. Mi sono occupato di individuare i parametri su cui poter intervenire: la risoluzione ottenibile applicando la matematica dell’olografia, le tecniche e gli algoritmi di inversione del campo elettromagnetico, lo studio dell’ambiente elettromagnetico irradiato e i requisiti dell’elemento radiante (tipo di antenna, forma, dimensioni, potenza irradiata) reailzzandone uno con la tecnologia della stampa tridimensionale. Ho valutato e studiato una soluzione per migliorare la compatibilità elettromagnetica con il sistema robotico su cui dovrà operare il RADAR. Per realizzare un prototipo funzionante mi sono occupato di definire i requisiti dell’elettronica di pilotaggio e della programmazione dei dispositivi implementati. Questo testo si conclude con la dimostrazione, mediante l’esposizione di prove sperimentali in ambiente controllato, delle prestazioni del nuovo RADAR, evidenziandone le differenze rispetto al HSR originale. ------------- Thanks to the funding obtained with the North Atlantic Treaty Organization, Science for Peace and Security (NATO SPS) G-5014 project, a multi-sensor robotic platform was developed capable of identifying buried plastic and metal objects and generating data for subsequent classification. of ordnance through the analysis of specialized operators. Using a robotic platform allows you to increase safety for operators, because it can be completely remotely controlled via a web software interface and allows you to use different sensors to maximize the probability of mine detection, while keeping the probability of receiving false alarms to a minimum. The main sensors installed are two RADARs operating in the microwave spectrum (≃2 GHz): a UWB Ground Penetrating RADAR (GPR), specially developed to detect the position of the buried object within the illuminated area, capable of detecting buried objects during the motion of the platform and a Holographic Subsurface RADAR (HSR), operating at continuous wave and single frequency, capable of generating holographic images that allow to observe the shape and dimensions of the objects buried in the first 15 - 20 cm of the subsoil and, through the processing with electromagnetic field inversion algorithms, it allows to reconstruct the three-dimensional scene that is in front of the synthetic opening of the RADAR. The images that this device generates allow to discriminate the bombs from other objects reflecting the microwaves but completely harmless (clutter). The HSR designed during the NATO SPS G-5014 project constitutes a first prototype that met the requirements of the project. The fruit of this work has attracted interest in the scientific community and at NATO SPS, generating a sequel: the NATO SPS G-5731 project, which is still underway. My work is part of this last project: I contributed to the development of a RADAR system for microwave images capable of improving, in terms of the quality of images produced (by increasing the signal-to-noise ratio and resolution) and depth of penetration (studying the electromagnetic characteristics of the soil of interest), the performance of the HSR. I worked on identifying the parameters on which to intervene: the resolution obtainable by applying the mathematics of holography, the techniques and algorithms of electromagnetic field inversion, the study of the radiated electromagnetic environment and the requirements of the radiant element (type of antenna , shape, size, radiated power) by realizing one with the technology of three-dimensional printing. I have evaluated and studied a solution to improve the electromagnetic compatibility with the robotic system on which the RADAR will have to operate. To create a working prototype, I worked on defining the requirements of the driving electronics and programming of the implemented devices. This text ends with the demonstration, through the display of experimental tests in a controlled environment, of the performance of the new RADAR, highlighting the differences compared to the original HSR.

In this paper we propose a programmable wavefront generation system using two binary phase spatial light modulators (BPSLMs). The output of the binary phase hologram has inversion symmetry and is restricted to be space–invariant, if the output of the hologram is viewed in the Fourier plane of a lens. Inversion symmetry may be broken by introducing a fixed binary phase hologram [1,2] but in this case diffraction efficiency ηd is not increased. Alternatively, an asymmetric output may be generated by increasing the number of phase levels [3]. Results obtained in this way increase ηd but the output remains space-invariant.

Optical volume holographic memories provide the potential for high storage capacity, parallel readout of data pages with short access times and high data transfer rates. Multiple image storage in a single region of a photorefractive crystal can be achieved using different addressing techniques as angular, wavelength, or phase-coded multiplexing. In combination with spatial multiplexing, volume holographic memories may achieve the storage of more than 1 Terabyte of information. Among these techniques, orthogonal phase-coded multiplexing [1] offers several advantages over angular and wavelength multiplexing, having the same storage capacity. A holographic data storage system based on phase-coded multiplexing operates with a fixed wavelength and a fixed geometry, avoiding mechanically moving parts. At the same time it provides short readout times and high energy efficiency. The signal-to-noise ratio of phase-coded multiplexing for a given number of holograms is more than two orders of magnitude higher than for angular and wavelength multiplexing [2]. Moreover, it allows to perform arithmetic operations as addition and subtraction of two or more data pages directly during readout of the memory [3]. Image processing operations like comparison of two stored images or image inversion and the logical operations OR, XOR and NOT with digital data pages can be realized in that way. Therefore, using phase-coded optical memories, high capacity data storage and high speed data processing becomes possible simultaneously.