Showing papers on "Fresnel zone published in 2014"
TL;DR: In this article, a superoscillatory focusing lens has been demonstrated by optimizing Fresnel zone plates (FZP), with limited physical insight as to how the lens feature contributes to the focal formation.
Abstract: A superoscillatory focusing lens has been experimen- tally demonstrated by optimizing Fresnel zone plates (FZP), with limited physical insight as to how the lens feature contributes to the focal formation. It is therefore imperative to establish a generalized viable account for both FZP (amplitude mask) and binary optics (phase mask). Arbitrary superoscillatory spots can now be customized and realized by a realistic optical device, without using optimization. It is counterintuitively found that high spatial frequency with small amplitude and destructive interfer- ence are favorable in superfocusing of a superoscillation pat- tern. The inevitably high sidelobe is pushed 15λ away from the central subwavelength spot, resulting in significantly enlarged field of view for viable imaging applications. This work therefore not only reveals the explicit physical role of any given metallic/
143 citations
TL;DR: A type of Fresnel zone plate in which its phase is shifted radially outward can easily and precisely turn an incident plane wave into an annular beam at its focal plane and the width of the annulus is a function of focal length.
Abstract: We introduce a type of Fresnel zone plate (FZP) in which its phase is shifted radially outward. This FZP can easily and precisely turn an incident plane wave into an annular beam at its focal plane. High efficiency and flexibility are the advantages of generating doughnut beams by this method. By performing direct calculations and using Bessel function properties, it is shown that a radially shifted zone plate produces annulus focus. Furthermore, by simulating the modified phase structure, in addition to demonstrating the formation of a ring-shaped focus, we also showed that its radius merely depends on the amount of the shift. We also showed that the width of the annulus is a function of focal length. Simulation results were thoroughly examined by experiments. Finally, it is clearly revealed that at a certain distance from the focal plane along the beam propagation, an annular beam is transformed into a Bessel beam, and a focal line is formed.
46 citations
TL;DR: An extremely compact soft x-ray microscope operating in the "water window" region at the wavelength λ = 2.88 nm is presented, making use of a long-term stable and nearly debris-free laser-induced plasma from a pulsed nitrogen gas jet target.
Abstract: An extremely compact soft x-ray microscope operating in the "water window" region at the wavelength λ = 2.88 nm is presented, making use of a long-term stable and nearly debris-free laser-induced plasma from a pulsed nitrogen gas jet target. The well characterized soft x-ray radiation is focused by an ellipsoidal grazing incidence condenser mirror. Imaging of a sample onto a CCD camera is achieved with a Fresnel zone plate using magnifications up to 500x. The spatial resolution of the recorded microscopic images is about 100 nm as demonstrated for a Siemens star test pattern.
46 citations
TL;DR: High-efficiency nanofocusing of hard X-rays using stacked multilevel Fresnel Fresnel zone plates with the smallest zone width of 200 nm is demonstrated.
Abstract: High-efficiency nanofocusing of hard X-rays using stacked multilevel Fresnel zone plates with a smallest zone width of 200 nm is demonstrated. The approach is to approximate the ideal parabolic lens profile with two-, three-, four- and six-level zone plates. By stacking binary and three-level zone plates with an additional binary zone plate, the number of levels in the optical transmission function was doubled, resulting in four- and six-level profiles, respectively. Efficiencies up to 53.7% focusing were experimentally obtained with 6.5 keV photons using a compact alignment apparatus based on piezoelectric actuators. The measurements have also been compared with numerical simulations to study the misalignment of the two zone plates.
43 citations
TL;DR: The reconstructed focal spots demonstrate good agreement with the theoretically expected wavefields and diffraction-limited focusing.
Abstract: We have characterized the x-ray phase vortices generated at the focal spot of various spiral Fresnel zone plates with an outermost zone width of Δr=50 nm. The complex-valued wavefields of phase vortices as small as 50 nm in size (FWHM) and several topological charges were reconstructed using ptychographic coherent diffractive imaging. The reconstructed focal spots demonstrate good agreement with the theoretically expected wavefields and diffraction-limited focusing.
39 citations
TL;DR: To increase the number of FZPs within one stack, this work demonstrates intermediate-field stacking and maximized efficiencies for high resolution focusing at three different energies, 10, 11.8, and 25 keV.
Abstract: Focusing efficiency of Fresnel zone plates (FZPs) for X-rays depends on zone height, while the achievable spatial resolution depends on the width of the finest zones. FZPs with optimal efficiency and sub-100-nm spatial resolution require high aspect ratio structures which are difficult to fabricate with current technology especially for the hard X-ray regime. A possible solution is to stack several zone plates. To increase the number of FZPs within one stack, we first demonstrate intermediate-field stacking and apply this method by stacks of up to five FZPs with adjusted diameters. Approaching the respective optimum zone height, we maximized efficiencies for high resolution focusing at three different energies, 10, 11.8, and 25 keV.
32 citations
TL;DR: The ability to fabricate 4-level diffractive structures with 1 µm critical dimensions has been demonstrated for the creation of fast Fresnel zone lenses with >60% diffraction efficiency into the -1 focusing order and nearly complete suppression of 0 and +1 orders.
Abstract: The ability to fabricate 4-level diffractive structures with 1 µm critical dimensions has been demonstrated for the creation of fast (∼f/3.1 at 633 nm) Fresnel zone lenses (FZLs) with >60% diffraction efficiency into the −1 focusing order and nearly complete suppression of 0 and +1 orders. This is done using tooling capable of producing optics with 800 mm apertures. A 4-level grating fabricated in glass at 300 mm aperture is shown to have <15 nm rms holographic phase error. Glass FZLs have also been used as mandrels for casting zero-thermal-expansion, 20 µm thick polymer films created with the 4-level structure as a route to mass replication of efficient diffractive membranes for ultralight segmented space-based telescope applications.
31 citations
TL;DR: The proposed binary-phase LCFZL manifests 39% diffraction efficiency at the focal point, which is close to the theoretical limit, 41%, and could find application in many modern devices.
Abstract: In this article, we disclose a method to fabricate a liquid crystal (LC) Fresnel zone lens (FZL) with high efficiency. The LCFZL, based on patterned planar-aligned regions, has been prepared by means of a two-step photoalignment technique. The proposed binary-phase LCFZL manifests 39% diffraction efficiency at the focal point, which is close to the theoretical limit, 41%. Moreover, because of a lower driving voltage and faster response time, these elements could find application in many modern devices.
30 citations
TL;DR: In this article, the authors developed triple layer on-chip stacked zone plates with an overlay accuracy of sub-2 nm which fulfills the nanofabrication requirements of X-ray optics.
Abstract: Fresnel zone plates are the key optical elements for nanoscale focusing of X-ray beams with high spatial resolution Conventional zone plates manufactured by planar nanotechnology processes are limited by the achievable aspect ratios of their zone structures Additionally, ultra-high resolution X-ray optics with high efficiency requires three-dimensional (3-D) shaped tilted zones The combination of high spatial resolution and high diffraction efficiency is a fundamental problem in X-ray optics Based on electrodynamical simulations, we find that the optimized zone plate profile for volume diffraction is given by zone structures with radially increasing tilt angles and decreasing zone heights On-chip stacking permits the realization of such advanced 3-D profiles without significant loss of the maximum theoretical efficiency We developed triple layer on-chip stacked zone plates with an overlay accuracy of sub-2 nm which fulfills the nanofabrication requirements Efficiency measurements of on-chip stacked zone plates show significantly increased values compared to conventional zone plates
29 citations
TL;DR: A nano-focusing module based on two linear Fresnel zone plates is presented, designed to generate a kinoform phase profile in tilted geometry, thus overcoming the efficiency limitations of binary diffractive structures.
Abstract: A nano-focusing module based on two linear Fresnel zone plates is presented. The zone plates are designed to generate a kinoform phase profile in tilted geometry, thus overcoming the efficiency limitations of binary diffractive structures. Adjustment of the tilt angle enables tuning of the setup for optimal efficiency over a wide range of photon energies, ranging from 5 to 20 keV. Diffraction efficiency of more than 50% was measured for the full module at 8 keV photon energy. A diffraction limited spot size of 100 nm was verified by ptychographic reconstruction for a lens module with a large entrance aperture of 440 μm × 400 μm.
27 citations
TL;DR: It is demonstrated here, that two multilayer type FZPs, delivered from the sameMultilayer deposit, focus both hard and soft X-rays with high fidelity, and the results prove that these lenses can achieve at least 21 nm half-pitch resolution at 1.2 keV.
Abstract: X-ray microscopy is a successful technique with applications in several key fields. Fresnel zone plates (FZPs) have been the optical elements driving its success, especially in the soft X-ray range. However, focusing of hard X-rays via FZPs remains a challenge. It is demonstrated here, that two multilayer type FZPs, delivered from the same multilayer deposit, focus both hard and soft X-rays with high fidelity. The results prove that these lenses can achieve at least 21 nm half-pitch resolution at 1.2 keV demonstrated by direct imaging, and sub-30 nm FWHM (full-pitch) resolution at 7.9 keV, deduced from autocorrelation analysis. Reported FZPs had more than 10% diffraction efficiency near 1.5 keV.
TL;DR: Wang et al. as discussed by the authors presented a scheme to reconstruct sectional images in OSH with enhanced depth resolution, where a spatial light modulator (SLM) is adopted as a configurable point pupil.
Abstract: The optical scanning holography (OSH) technique can capture all the three-dimensional volume information of an object in a hologram via a single raster scan. The digital hologram can then be processed to reconstruct individual sectional images of the object. In this paper, we present a scheme to reconstruct sectional images in OSH with enhanced depth resolution, where a spatial light modulator (SLM) is adopted as a configurable point pupil. By switching the SLM between two states, different Fresnel zone plates (FZPs) are generated based on the same optical system. With extra information provided by different FZPs, a depth resolution at 0.7 μm can be achieved. © 2014 Chinese Laser Press
TL;DR: It is found that random errors significantly decrease the contrast transfer of X-ray microscopes and an upper bound for the mean acceptable variance of the deposition rate is derived.
Abstract: Fresnel zone plates produced by electron beam lithography and planar etching techniques provide a resolving power of about 10 nm. An alternative zone plate fabrication approach is based on alternately coating a micro-wire with two different materials. With this process, very thin zone layers with very high aspect ratios can be deposited. However, depending on the fabrication method, random zone positioning errors may introduce strong aberrations. We simulate the effect of positioning errors using different random fluctuations and study their influence on zone plate resolution. We find that random errors significantly decrease the contrast transfer of X-ray microscopes. Additionally, we derive an upper bound for the mean acceptable variance of the deposition rate.
28 Jan 2014
TL;DR: A novel computational photon sieve imaging modality that enables high-resolution spectral imaging and suggests that higher spatial and spectral resolution can be achieved as compared to conventional spectral imagers.
Abstract: Photon sieves, modifications of Fresnel zone plates, are a new class of diffractive image forming devices that open up new possibilities for high resolution imaging and spectroscopy, especially at UV and x-ray regime. In this paper, we develop a novel computational photon sieve imaging modality that enables high-resolution spectral imaging. For the spatially incoherent illumination, we study the problem of recovering the individual spectral images from the superimposed and blurred measurements of the proposed photon sieve system. This inverse problem, which can be viewed as a multi frame deconvolution problem involving multiple objects, is formulated as a maximum posterior estimation problem, and solved using a fixed-point algorithm. The performance of the proposed technique is illustrated for EUV spectral imaging through numerical simulations. The results suggest that higher spatial and spectral resolution can be achieved as compared to conventional spectral imagers.
11 Dec 2014-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a fast mechanical transfocator based on a compound refractive lens, which actively varies the number of individual lenses in the beam path to focus and image a time-of-flight beam, was presented.
Abstract: Thermal neutron beams are an indispensable tool in physics research. The spatial and the temporal resolution attainable in experiments are dependent on the flux and collimation of the neutron beam which remain relatively poor, even for modern neutron sources. These difficulties may be mitigated by the use of optics for focusing and imaging. Refractive and diffractive optical elements, e.g. compound refractive lenses and Fresnel zone plates, are attractive due to their low cost, and simple alignment. These optical elements, however, suffer from chromatic aberration, which limit their effectiveness to highly monochromatic beams. This paper presents two novel concepts for focusing and imaging non-monochromatic thermal neutron beams with well-known optical elements: (1) a fast mechanical transfocator based on a compound refractive lens, which actively varies the number of individual lenses in the beam path to focus and image a time-of-flight beam, and (2) a passive optical element consisting of a compound refractive lens, and a Fresnel zone plate, which may focus and image both continuous and pulsed neutron beams. (C) 2014 Elsevier B.V. All rights reserve (Less)
TL;DR: An analytical model of vector formalism is proposed to investigate the diffraction of high numerical aperture subwavelength circular binary phase Fresnel zone plate (FZP) and shows good agreement with those obtained by the finite-difference time-domain (FDTD) method within the effective extent of etch depth.
Abstract: An analytical model of vector formalism is proposed to investigate the diffraction of high numerical aperture subwavelength circular binary phase Fresnel zone plate (FZP). In the proposed model, the scattering on the FZP's surface, reflection and refraction within groove zones are considered and diffraction fields are calculated using the vector Rayleigh-Sommerfeld integral. The numerical results obtained by the proposed phase thick FZP (TFZP) model show a good agreement with those obtained by the finite-difference time-domain (FDTD) method within the effective extent of etch depth. The optimal etch depths predicted by both methods are approximately equal. The analytical TFZP model is very useful for designing a phase and hybrid amplitude-phase FZP with high-NA and short focal length.
TL;DR: Experimental results confirm the generation of a wavelength-independent ring pattern at the focus of the rf-FZL, which is found to be quasi-achromatic, in that the diameter is wavelength independent but its location is not.
Abstract: The phase of a standard Fresnel zone lens (FZL) is periodically modulated in the radial direction using the phase of a binary fraxicon. The resulting element (rf-FZL) focuses light into a ring. The ring is found to be quasi-achromatic, in that the diameter is wavelength independent but its location is not. The binary rf-FZL is fabricated using electron beam direct writing. Experimental results confirm the generation of a wavelength-independent ring pattern at the focus of the rf-FZL. An efficiency of 24% was obtained. The variation in radius of ring pattern was reduced from 61 μm to less than 10 nm for a corresponding wavelength variation from 532 to 633 nm.
TL;DR: In this article, a method for determining the center of scattering points of a multipath is proposed, provided that the direction of arrival of the multipath was known by the receiver.
TL;DR: In this paper, an exact solution for the complex field of transition radiation (TR) emitted by an electron incident on a conductive screen is presented, and the solution is valid in all space.
Abstract: We present an exact solution for the complex field of transition radiation (TR) emitted by an electron incident on a conductive screen. The solution is valid in all space. In the reactive near zone, it replicates the Coulomb fields of the electron and its image charge and their evolution into radiation fields after termination of the charge’s current at the screen. Using a general formulation for radiation diffraction from a current line, we derive diffraction integral expressions in the reactive near zone, the Fresnel near zone, and the Fraunhofer far zone in analogy to diffraction from a planar radiation source. The derived exact complex field expressions can be useful for describing coherent optical TR from a beam of phase-correlated charge particles in the near field and in the imaging plane of the screen.
TL;DR: It is shown that lateral resolution of the axilens is increased due to the replacement of circular zones, and by implementing different distributions of pinholes resolution and focal depth are changed and hence, are manageable.
Abstract: An axilens is a combination of an axicon and a Fresnel zone plate to provide a long focal diffractive lens. However, the photon sieve has been known as a high-resolution version of the Fresnel zone plate. Therefore, construction of an axilens on the basis of a photon sieve may yield a high-resolution axilens. To this end, circular zones of an axilens were replaced by a given distribution of pinholes. It is shown that lateral resolution of the axilens is increased due to the replacement. The impact of different distributions of pinholes on the focusing properties of the axilens were also examined. Results indicate that by implementing different distributions of pinholes resolution and focal depth are changed and hence, are manageable. Theoretical results are verified by experimental work.
TL;DR: An analysis of the optical performance of the aFZP based on scalar diffraction theory and numerical results for the light distribution in the focal plane are presented and complemented by calculations of the Optical transfer function.
Abstract: A conventional Fresnel zone plate (FZP) consists of concentric rings with an alternating binary transmission of zero and one. In an azimuthally structured Fresnel zone plate (aFZP), the light transmission of the transparent zones is modulated in the azimuthal direction, too. The resulting structure is of interest for extreme ultraviolet and x-ray imaging, in particular, because of its improved mechanical stability as compared to the simple ring structure of an FZP. Here, we present an analysis of the optical performance of the aFZP based on scalar diffraction theory and show numerical results for the light distribution in the focal plane. These will be complemented by calculations of the optical transfer function.
TL;DR: In this paper, a flat-ring Fresnel zone (CFZ) lens of flat dielectric rings was proposed and compared to a PFZ lens, a refractive plane-hyperbolic (PH) lens, and a conventional PH lens.
Abstract: Conical in shape Fresnel zone (CFZ) lens of flat dielectric rings is introduced and studied in this research. It is contrasted to a plane Fresnel zone (PFZ) lens, a CFZ lens of conical rings and a refractive plane-hyperbolic (PH) lens. For the same aperture diameter of about 25 mm and focal length of 30 mm, a 229-GHz CFZ lens of flat rings with a 30-degree opening semi-angle significantly surpasses the PFZ and PH lenses in focusing gain and efficiency. Also, it exhibits a subwavelength transverse resolution and much higher axial resolution. The cited 30-degree flat-ring CFZ lens has 4.5 times smaller weight than the PH lens, and is easy to manufacture as a plane multilayer package by means of precise machining or modern photolithographic and other microelectronic technologies. Nevertheless, the CFZ lens benefits over the corresponding PH refractive lens are attained on account of smaller frequency bandwidth and bigger lens thickness. The new flat-ring CFZ lens design can be applied in accurate imaging systems or for a creation of light and efficient microwave, terahertz and optical lens antennas.
TL;DR: Calculations using the Young-Maggi-Rubinowicz theory of diffraction yield analytical expressions for the amount of light spilling outside target areas due to diffraction at the edges of the concentrator Fresnel lenses.
Abstract: Fresnel lenses are widely used in concentrating photovoltaic (CPV) systems as primary optical elements focusing sunlight onto small solar cells or onto entrance apertures of secondary optical elements attached to the solar cells. Calculations using the Young-Maggi-Rubinowicz theory of diffraction yield analytical expressions for the amount of light spilling outside these target areas due to diffraction at the edges of the concentrator Fresnel lenses. Explicit equations are given for the diffraction loss due to planar Fresnel lenses with small prisms and due to arbitrarily shaped Fresnel lenses. Furthermore, the cases of illumination by monochromatic, polychromatic, totally spatially coherent and partially spatially coherent light (e.g. from the solar disc) are treated, resulting in analytical formulae. Examples using realistic values show losses due to diffraction of up to several percent.
TL;DR: Three-dimensional displacements of the object were determined by numerical back-propagation, or "refocusing" of the electromagnetic fields during the reconstruction of a single hologram during the fast oscillation of sub-micron cantilevers using time-resolved extreme ultraviolet (EUV) Fourier transform holography.
Abstract: We recorded the fast oscillation of sub-micron cantilevers using time-resolved extreme ultraviolet (EUV) Fourier transform holography. A tabletop capillary discharge EUV laser with a wavelength of 46.9 nm provided a large flux of coherent illumination that was split using a Fresnel zone plate to generate the object and the reference beams. The reference wave was produced by the first order focus while a central opening in the zone plate provided a direct illumination of the cantilevers. Single-shot holograms allowed for the composition of a movie featuring the fast oscillation. Three-dimensional displacements of the object were determined as well by numerical back-propagation, or "refocusing" of the electromagnetic fields during the reconstruction of a single hologram.
TL;DR: In this article, the authors describe the imaging capabilities of a 0.2 m membrane diffractive primary (DOE) used as a key element in FalconSat-7, a space-based solar telescope.
Abstract: We describe imaging capabilities of a 0.2 m membrane diffractive primary (DOE) used as a key element in FalconSat-7, a space-based solar telescope. Its mission is to take an image of the Sun at the H-alpha wavelength (656nm) over a narrow bandwidth while in orbit. In this case the DOE is a photon sieve which consists of billions of tiny holes, with the focusing ability dependent on an underlying Fresnel zone geometry. Uniform radial expansion/contraction of the substrate due to temperature or relative humidity change will result in a shift in focal length without introducing errors in phase of the transmitted wavefront and without a decrease in efficiency. We will also show that while ideally the DOE surface should be held flat to within 5.25 microns, an opto-mechanical analysis showed that local deformations up to 32 microns are possible without significantly degrading the image quality.
TL;DR: In this article, the surface plasmon focusing has been shown to achieve a sub-wavelength focusing effect with the focusing spot at a subwavelength scale, based on the principle of optical interference that the constructive superposition of SPs with phase matching can result in a considerable electric-field enhancement of SP in the near field.
Abstract: In this review, we show that by designing the metallic nanostructures, the surface plasmon (SP) focusing has been achieved, with the focusing spot at a subwavelength scale. The central idea is based on the principle of optical interference that the constructive superposition of SPs with phase matching can result in a considerable electric-field enhancement of SPs in the near field, exhibiting a pronounced focusing spot. We first reviewed several new designs for surface plasmon focusing by controlling the metallic geometry or incident light polarization: We made an in-plane plasmonic Fresnel zone plates, a counterpart in optics, which produces an obvious SP focusing effect; We also fabricated the symmetry broken nanocorrals which can provide the spatial phase difference for SPs, and then we propose another plasmon focusing approach by using semicircular nanoslits, which gives rise to the phase difference through changing refractive index of the medium in the nanoslits. Further, we showed that the spiral metallic nanostructure can be severed as plasmonic lens to control the plasmon focusing under a linearly polarized light with different angles.
TL;DR: In this article, the exact vector angular spectrum (VAS) was used to analyze the near-field focusing properties of actual hybrid amplitude-phase binary subwavelength Fresnel zone plates (HBSFZPs).
Abstract: The near-field focusing properties of actual hybrid amplitude–phase binary subwavelength Fresnel zone plates (HBSFZPs) are studied theoretically. The analysis based on the exact vector angular spectrum method is done for a radially polarized beam incident on the HBSFZPs. The results show that the near-field subwavelength focusing with a long depth of focus can be obtained using an HBSFZP, which is very useful for near-field subwavelength photolithography and high-resolution microscopy. The position of the actual focus in the near-field focusing HBSFZPs depends on the evanescent wave rather than the propagating wave. The etch depth has an important influence on focusing properties of HBSFZPs.
TL;DR: In this article, the influence of shadowing on the focusing properties of binary phase Fresnel zone plates (FZPs) was studied using the vector diffraction theory and the results showed that a low-numerical-aperture (NA) FZP can be treated as an ideal in-plane FZPs and the shadowing effect can be neglected.
TL;DR: By using a gold bowtie nanoantenna at the focal plane of a plasmonic Fresnel zone plate lens, it is numerically demonstrated that the focused beam spot can be strongly confined in a three-dimensional (3D) region.
Abstract: By using a gold bowtie nanoantenna at the focal plane of a plasmonic Fresnel zone plate lens, we numerically demonstrate that the focused beam spot can be strongly confined in a three-dimensional (3D) region, which means the focal spot will have high axial resolution as well as high lateral resolution. According to the antenna’s resonance spectrum, the Fresnel zone plate lens is designed at the resonance wavelength of the antenna to get the right diffractive efficiency, and then the antenna will be positioned at the focal plane, so the 3D confined focal spot can be achieved with much higher intensity and much smaller spot size along both axial and transverse directions than that of a lens without using antennas.
01 Jan 2014
TL;DR: In this paper, a study on a class of algorithms based on Uniform Theory of Diffraction (UTD) for multiple diffractions is presented, where the authors show how relative permittivity constant, conductivity and inner angle of wedge and polarization type affect the relative path loss.
Abstract: This paper presents a study on a class of algorithms based on Uniform Theory of Diffraction (UTD) for multiple diffractions. Within this context Slope UTD with Convex Hull (S-UTD-CH) model based on Slope UTD and Fresnel zone concept was reviewed. S-UTD-CH model can be used for fast and more accurate field prediction for multiple diffractions in transition zone. An extensive simulation results for comparison of UTD based algorithms with respect to the computation time and accuracy was provided. Furthermore, the study shows how relative permittivity constant, conductivity and inner angle of wedge and polarization type affect the relative path loss.