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Acoustic vortex beams, which have both linear and angular momentum, can be used to make precise acoustic tweezers. Limited by the symmetry of a normal vortex beam, these tweezers are usually used for trapping or rotating particles in two dimensions. Here, the three-dimensional spiral motion of two soft particles of different sizes was realized using a vortex beam with a twisted focus, which was synthesized by a silicone binary-phase logarithmic-spiral zone plate. Numerical simulations and experimental measurements demonstrated that the beam had anisotropic focuses of crescent transverse intensity profiles and a screw phase dislocation with a singularity at the center. Experiments showed that a small particle (k0r ≈ 1.3) can follow the twisted intensity of the beam, but a large particle (k0r ≈ 4.7) spirals up away from the twisted field pattern. This is attributed to the dominant gradient force for the small particle, whereas the scattering effect induced a scattering force combined with a gradient force for the large particle. This focused twisted beam, which was generated with a structured silicone plate, and the three-dimensional spiral motion of microparticles, advance the development of simple, compact, and disposable acoustic devices for the precise and diverse manipulation of microparticles.

This conference paper presents a dual-band aperture-shared Fresnel zone plate (FZP)-based lens antenna for the V-band and D-band applications using conductive and dielectric fully-integrated 3D printing. In contrast to traditional full metal-based structures, double-screen grid structures are used to implement the concentric opaque rings of the FZP. Since the grids provide different transmission/reflection features at dual-band, they will not influence each other. A dielectric ring is directly printed atop the FZP for compensating for the phase-shifting from the grids. An antenna prototype is fabricated and measured. The radiation performance agrees well. The peak gains achieved are 20.3 dBi for the V-band and 21.9 dBi for the D-band, respectively.

International audience; An important challenge in infrared imaging today consists in addressing the SWaP problem (Size, Weight and Power), for example by simplifying as much as possible the optical system before the sensor. The work presented in this paper takes advantage of recent techniques in femtosecond laser direct writing to imprint optical systems. This work aims at merging a lens array with a filter array by writing gradient index lenses with a femtosecond laser inside a dedicated glass substrate. A classical gradient index lens requires a huge refractive index variation, which cannot be reached today with femtosecond laser processing (Δnmax ~ 0,05). So, we decided to turn towards writing a gradient index Fresnel lens. A first-order Fresnel lens was designed with a Δnmax < 5.10−2 discretised into 8 index levels to guarantee a diffraction efficiency of 85% on the overall spectral bandwidth of the filters. We studied a chalcogenide glass because of his good properties in mid-IR optics. We compared the different laser responses of the material: threshold of permanent changes, quantitative phase and index variation. Finally, we showed that reaching a phase variation of π radians with femtosecond laser writing is possible even for a huge scanning speed (0,01 mm/s up to 25 mm/s). By overlapping the written lines, we were able to implement a maximum phase variation of 8 radians (with only one written layer), demonstrating the possibility to write quickly a GRIN Fresnel lens with a diameter of some millimeters.; Un défi important dans l'imagerie infrarouge consiste aujourd'hui à résoudre le problème SWaP (Size, Weight and Power), par exemple en simplifiant autant que possible le système optique avant le capteur. Le travail présenté dans cet article tire parti des techniques récentes de texturation par laser femtoseconde pour créer des systèmes optiques. Ce travail vise à fusionner une matrice de lentilles avec une matrice de filtres en écrivant des lentilles à gradient d'indice avec un laser femtoseconde dans un substrat dédié. Une lentille classique à gradient d'indice nécessite une variation importante de l'indice de réfraction, qui ne peut être atteinte aujourd'hui avec une fabrication par laser femtoseconde (Δn ~ 0,05). Nous avons donc décidé de nous tourner vers l'écriture d'une lentille de Fresnel à gradient d'indice. Une lentille de Fresnel du premier ordre a été conçue avec un Δn < 5e-2 discrétisé en 8 niveaux d'indice afin de garantir une efficacité de diffraction de 85% sur la bande passante spectrale globale des filtres. Nous avons étudié un verre de chalcogénure en raison de ses bonnes propriétés optiques dans le moyen infrarouge. Nous avons comparé les différentes réponses laser du matériau : seuil de changements permanents, variation quantitative de phase et d'indice. Enfin, nous avons montré qu'atteindre une variation de phase de π radians avec une texturation laser femtoseconde est possible même pour une vitesse d'écriture très élevée (0,01 mm/s à 25 mm/s). En superposant légèrement les lignes texturées, nous avons pu mettre en œuvre une variation de phase maximale de 8 radians (avec une seule couche), démontrant la possibilité d'écrire rapidement une lentille de Fresnel GRIN d'un diamètre de quelques millimètres.

An optical asymmetric cryptosystem built on chaotic zone plate phase mask (CZPPM) has been proposed. Here the pixels of an image are shuffled by employing Arnold transform \(\left( {{\text{AT}}^{\omega } } \right)\) and is then modulated with the CZPPM featuring in the gyrator Transform domain (GT). This increases randomness and adds chaotic parameters that make the system highly secure. The proposed system strengthens the security of the cryptosystem and does not permit the attacker to retrieve the initial image without the expertise of keys. The robustness of the projected cryptosystem has been investigated and validated based on an extra degree of freedom by simulating on MATLAB 9.9.0 (R2020b), and investigational outcomes have been shown to emphasize the efficacy of the algorithm.

High-aspect ratio silicon (Si) nanostructures are important for many applications. Metal-assisted chemical etching (MACE) is a wet-chemical method used for the fabrication of nanostructured Si. Two main challenges exist with etching Si structures in the nanometer range with MACE: keeping mechanical stability at high aspect ratios and maintaining a vertical etching profile. In this work, we investigated the etching behavior of two zone plate catalyst designs in a systematic manner at four different MACE conditions as a function of mechanical stability and etching verticality. The zone plate catalyst designs served as models for Si nanostructures over a wide range of feature sizes ranging from 850 nm to 30 nm at 1:1 line-to-space ratio. The first design was a grid-like, interconnected catalyst (brick wall) and the second design was a hybrid catalyst that was partly isolated, partly interconnected (fishbone). Results showed that the brick wall design was mechanically stable up to an aspect ratio of 30:1 with vertical Si structures at most investigated conditions. The fishbone design showed higher mechanical stability thanks to the Si backbone in the design, but on the other hand required careful control of the reaction kinetics for etching verticality. The influence of MACE reaction kinetics was identified by lowering the oxidant concentration, lowering the processing temperature and by isopropanol addition. We report an optimized MACE condition to achieve an aspect ratio of at least 100:1 at room temperature processing by incorporating isopropanol in the etching solution.

A modified interfering vortex spiral zone plate (MIVSZP) is proposed to produce two polygon-like beams at the focal plane. A radial shift parameter t3 has influence on the shapes of two beams. When t3 has an appropriate value only, the MIVSZP has two polygon-like beams. With the increase of the inner phase modulation parameter t1, the rotation angle of the inner polygon-like beam increases firstly, then decreases and increases finally. When the outer phase modulation parameter t2 increases, the rotation angle of the inner polygon-like beam increases. However, t1 and t2 cannot make the outer polygon-like beam rotate. The topological charge p of the modified interfering vortex phase is equal to the number of sides of the polygon. In addition, for the arbitrary topological charge l of the spiral zone plate, the two polygon-like beams have the same topological charge equal to l. Moreover, it is proved in the simulations and experiments that the topological charges of two polygon-like beams can be identified by the number of fringes or spots generated by the interference binary phase transmittance. The method of constructing the MIVSZP is illustrated. The proposed zone plate is applicable to rotate particles located at different polygons simultaneously, and increase optical communication capacities.

Herein, we are about to introduce a novel, reliable and straightforward method to create controllable dark lines employing an azimuthal square zone plate. As a matter of fact, this diffractive element is a square zone plate whose zones are phase-shifted azimuthally. As we illustrate, one way to construct it is combining a square zone plate and radial grating having period m. Considering its focusing behavior, we came to the result that a dark line surrounded by linear bright zones is generated for odd m, as well as a cross-like dark zone is produced when m is even. Furthermore, we illustrate that the length of the dark lines depends on the grating period. Finally, the simulation predictions are verified by experimental results.

We acquired high resolution images of laser driven cylindrical implosion experiments using a Fresnel zone plate (FZP), a diffraction driven lens composed of alternating opaque and transparent rings, on the OMEGA laser at the Laboratory for Laser Energetics in Rochester, NY, USA. Our FZP geometrical properties were designed for a standard 25x magnification and include 700 zones of 900 nm thick gold, minimum zone width of 40 nm, and a lens radius of 56 μm to focus an energy spectral peak at 6.127 keV emitted from a Manganese backlighter. This design was informed by our new Python-implemented forward model that considers 4 diffractive orders and a realistic x-ray spectrum to characterize the spatial resolution of FZP systems. The model supports two methods of exploring FZP designs: optimization via the SciPy library and algorithmic differentiation via the PyTorch library and its neural network module.

In this work we present a powerful and efficient technique to generate structured acoustic beams, e.g., vortex beams, by means of active-spiral diffraction gratings that are driven by electrical signals and operated as a single radiator. The main feature of this technique is the capacity to work over a broad range of frequencies, i.e., from 70 kHz to beyond 300 kHz, in air. By varying the excitation frequency, a fine and continuous tuning of the focal length of the acoustic vortex is achieved, and as a result, the vortex beams generated can be axially steered while their spatial distribution is preserved. To experimentally demonstrate these features, two prototypes are presented: the Archimedean spiral, and the Spiral Fresnel Zone Plate. The former can generate simultaneous higher order Bessel beams with different topological charge along the propagation axis. The latter allows us to create sharp focused vortex beams. The experiments show a good agreement in comparison with simulations. The versatility and simplicity of the device make it highly suitable and with a potential in emerging applications such as particle manipulation, acoustic imaging, transfer of angular momentum to matter, acoustic communication, and biomedical applications.

[EN] In this work, we analyze the effect of the distribution of transparent Fresnel regions over the focusing profile of Soret Zone Plates (SZP) based on binary sequences. It is shown that this effect becomes very significant in those fields where directional transducers are employed, such as microwaves or acoustics. A thorough analysis of both the SZP transmission efficiency and the focusing enhancement factor is presented. Moreover, experimental measurements are also carried out for a particular type of binary sequence, the Cantor ternary set, validating the theoretical model and demonstrating that the distribution of transparent Fresnel regions becomes a critical parameter in applications requiring directional emitters., This work has been supported by Spanish MICINN RTI2018-100792-B-I00 project and Generalitat Valenciana AICO/2020/139 project.

A nonmagnetic Fresnel Zone Plate Lens (FZPL) antenna with high dielectric plastic porosity controlling is proposed in this paper. Compared to conventional Fresnel plates, the proposed structure has a single homogeneous platform for transmitting mode role, making the gradient refractive index lens antenna a perfect candidate for high gain applications. A non-magnetic plastic has achieved the intended GRIN subzones homogeneously. Each desired permittivity for half-wave plate subzones is estimated with a capacitive estimation on Brakora analysis. Half-wave zone type of FZP is selected to utilize based on optic rules to realize this estimation. A Cos41-like conical horn is used as a central beam-launcher to excite the lens diaphragms and was implemented and measured at 30 GHz. The measured scattering parameters for ZP shows a better than −15 dB return loss and validate our modeling with 5 mm thickness and $3\lambda_{0}$ lateral dimension.

[EN] In this work, we analyze the effect of predistortion techniques on the focusing profile of Fresnel Zone Plates (FZPs) in ultrasound applications. This novel predistortion method is based on either increasing or decreasing the width of some of the FZP Fresnel rings by a certain amount. We investigate how the magnitude of the predistortion, as well as the number and location of the predistorted rings, influences the lens focusing profile. This focusing profile can be affected in different ways depending on the area of the lens where the predistortion is applied. It is shown that when the inner area of the lens, closer to its center, is predistorted, this technique allows the control of the focal depth at the main focus. However, when the predistortion is applied to an area farther from the center of the lens, the acoustic intensity distribution among the main focus and the closest adjacent secondary foci can be tailored at a certain degree. This predistortion technique shows great potential and can be used to control, modify and shape the FZP focusing profile in both industrial and therapeutic applications., This work has been supported by Spanish MICINN RTI2018-100792-B-I00 project and Generalitat Valenciana AICO/2020/139 project.

In recent years, integral imaging has received increasing attention as a promising 3D imaging technique with one single exposure. In medical diagnostics, the X-ray integral imaging system potentially has a much shorter exposure time than the conventional computed tomography, reducing the radiation damage to the patient. By replacing the micro-lens array with a micro-Fresnel Zone Plate (FZP) array, the classical visible integral imaging system can be transposed to an X-ray system. However, limited by the micro-scale dimensions of FZP in the array and current manufacturing techniques, the number of zones of FZP is required to be small. This may have an important impact on the FZP imaging performance. Based on the scalar diffraction theory, this paper introduces a simulation method and numerically investigated the effect of the number of zones on the FZP imaging performance under different coherence conditions.

Lensless imaging requires coherent illumination, which is typically available at beamlines. A study of lensless imaging with a table-top X-ray laser is presented, comparing two alternative data-processing techniques, i.e. using the near and the far field data. In order to have a consistent comparison, a Fresnel zone plate was studied as object, because its modulated structure permits to obtain both Fresnel (near field) and Fraunhofer (far field) pattern simultaneously. Results show factor of 3 difference in imaging resolution, and a major limitation given by the degree of the illumination homogeneity.