Showing papers on "Fresnel zone published in 2015"
TL;DR: In this paper, a flat and ultrathin lenses based on graphene, the world's thinnest known material, were presented, and the working of the lenses and their performance in the visible and terahertz regimes were analyzed computationally.
Abstract: Flat lenses when compared to curved surface lenses have the advantages of being aberration free, and they offer a compact design necessary for a myriad of electro-optical applications. In this paper we present flat and ultrathin lenses based on graphene, the world’s thinnest known material. Monolayers and multilayers of graphene were fabricated into Fresnel zones to produce Fresnel zone plates, which utilize the reflection and transmission properties of graphene for their operation. The working of the lenses and their performance in the visible and terahertz regimes were analyzed computationally. Experimental measurements were also performed to characterize the lens in the visible regime, and a good agreement was obtained with the simulations. This work demonstrates the principle of atom-thick graphene-based lenses, with perspectives for ultracompact integration.
73 citations
TL;DR: A method for using thin nanostructured plasmonic metasurfaces to design diffractive Fresnel zone plate lenses that focus pairs of wavelengths to a single focal point to address any superposition of the two colors at the focus of the lenses by controlling the polarization of light.
Abstract: We demonstrate experimentally and by simulations a method for using thin nanostructured plasmonic metasurfaces to design diffractive Fresnel zone plate lenses that focus pairs of wavelengths to a single focal point. The metasurfaces are made of tightly packed cross and rod shaped optical nanoantennas with strong polarization and wavelength selectivity. This selectivity allows multiplexing two different lenses with low spectral crosstalk on the same substrate and to address any superposition of the two colors at the focus of the lenses by controlling the polarization of light. This concept can open the door to use ultrathin diffractive lenses in fluorescence microscopy and in stimulated emission depletion microscopy.
69 citations
TL;DR: In this paper, a non-uniform sinusoidally modulated half-mode microstrip structure with application to near-field focused leaky-wave radiation in the backward Fresnel zone is proposed.
Abstract: A novel non-uniform sinusoidally modulated half-mode microstrip structure with application to near-field focused leaky-wave radiation in the backward Fresnel zone is proposed First, it is presented a dispersion analysis of the constituent backward leaky wave in the sinusoidally modulated unit cell in half-width microstrip technology This information is then used to design a finite non-uniform line that focuses the radiated fields at the desired point Finally, eight similar line sources are arranged in a radial array to generate a three-dimensional focused spot located at the desired focal length over the simple central coaxial feeding Simulated and experimental results are presented to validate the proposed simple approach
55 citations
TL;DR: The proposed FLCFZLs with simple fabrication open several opportunities to improve the quality of existing devices and to find new applications, including the diffracting element, which provides fast response time, high diffraction efficiency, and saturated electro-optical operations up to high frequency.
Abstract: In this Letter, we disclose a fast switchable Fresnel zone lens (FZL) by confining the ferroelectric liquid crystals (FLCs) in multiple microscopically defined photo-aligned alignment domains. The photo-alignment (PA) offers good control on the anchoring energy (W) by mean of irradiation doses (ID) and thus excellent alignment for FLCs. Two operational modes of the FLCFZL, i.e., FOCUS/OFF and FOCUS/DEFOCUS, were demonstrated. The proposed diffracting element provides fast response time, high diffraction efficiency (η), with saturated electro-optical (EO) operations up to high frequency (≈2 kHz). Thus, the proposed FLCFZLs with simple fabrication open several opportunities to improve the quality of existing devices and to find new applications.
49 citations
TL;DR: The presented double-sided zone plates with 30 nm smallest zone width offer up to 9.9% focusing efficiency at 9 keV, that results in a factor of two improvement over their previously demonstrated single-sided counterparts.
Abstract: The fabrication of high aspect ratio metallic nanostructures is crucial for the production of efficient diffractive X-ray optics in the hard X-ray range We present a novel method to increase their structure height via the double-sided patterning of the support membrane In transmission, the two Fresnel zone plates on the two sides of the substrate will act as a single zone plate with added structure height The presented double-sided zone plates with 30 nm smallest zone width offer up to 99% focusing efficiency at 9 keV, that results in a factor of two improvement over their previously demonstrated single-sided counterparts The increase in efficiency paves the way to speed up X-ray microscopy measurements and allows the more efficient utilization of the flux in full-field X-ray microscopy
44 citations
TL;DR: In this article, the angle of diffracting layers smoothly varies in the lens to achieve optimum diffraction efficiency across the entire pupil of the lens, which can be used to extend the achievable numerical aperture of multilayer Laue lenses to reach considerably smaller focal spot sizes.
Abstract: We present a new method to fabricate wedged multilayer Laue lenses, in which the angle of diffracting layers smoothly varies in the lens to achieve optimum diffracting efficiency across the entire pupil of the lens. This was achieved by depositing a multilayer onto a flat substrate placed in the penumbra of a straight-edge mask. The distance between the mask and the substrate was calibrated and the multilayer Laue lens was cut in a position where the varying layer thickness and the varying layer tilt simultaneously satisfy the Fresnel zone plate condition and Bragg’s law for all layers in the stack. This method can be used to extend the achievable numerical aperture of multilayer Laue lenses to reach considerably smaller focal spot sizes than achievable with lenses composed of parallel layers.
38 citations
TL;DR: Arrays of Fresnel zone plates fabricated on a flexible substrate, which allows for the adjustment of both the field of view and optical focus are presented, which could be integrated with electronics and have a wide range of potential applications, from medical imaging to surveillance.
Abstract: Field of view and accommodative focus are two fundamental attributes of many imaging systems, ranging from human eyes to microscopes. Here, we present arrays of Fresnel zone plates fabricated on a flexible substrate, which allows for the adjustment of both the field of view and optical focus. Such zone plates function as compact and lightweight microlenses and are fabricated using silicon nanowires. Inspired by compound eyes in nature, these microlenses are designed to point along various angles in order to capture images, offering an exceptionally wide field of view. Moreover, by flexing the substrate, the lens position can be adjusted, thus achieving axial focus scanning. An array of microlenses on a flexible substrate was incorporated into an optical system to demonstrate high resolution imaging of objects located at different axial and angular positions. These silicon based microlenses could be integrated with electronics and have a wide range of potential applications, from medical imaging to surveillance.
38 citations
TL;DR: A single-pulse laser ablation technique to write parallel surface gratings and Fresnel zone plates to record a surface grating with 820 nm periodicity and asymmetric zone plate holograms on 4.5 nm gold-coated substrates is demonstrated.
Abstract: Holography plays a significant role in applications such as data storage, light trapping, security, and biosensors. However, conventional fabrication methods remain time-consuming, costly, and complex, limiting the fabrication of holograms and their extensive use. Here, we demonstrate a single-pulse laser ablation technique to write parallel surface gratings and Fresnel zone plates. We utilized a 6 ns high-energy green laser pulse to form interference patterns to record a surface grating with 820 nm periodicity and asymmetric zone plate holograms on 4.5 nm gold-coated substrates. The holographic recording process was completed within seconds. The optical characteristics of the interference patterns have been computationally modeled, and well-ordered polychromatic diffraction was observed from the fabricated holograms. The zone plate showed a significant diffraction angle of 32° from the normal incident for the focal point. The nanosecond laser interference ablation for rapid hologram fabrication holds great potential in a vast range of optical devices.
32 citations
TL;DR: In this paper, a simple and sensitive technique, based on Fresnel diffraction from phase objects, is proposed for specifying the nonlinear refractive index of a sample, which is obtained by measurement of the normalized intensity distribution of the Fresnel diffusion patterns.
Abstract: A simple and sensitive technique, based on Fresnel diffraction from phase objects, is proposed for specifying the nonlinear refractive index of a sample. In this technique, the nonlinear refractive index is obtained by measurement of the normalized intensity distribution of the Fresnel diffraction patterns. The fringe diffraction patterns are formed due to the propagating monochromatic plane wave beam through a phase object. The phase object is the result of the changes in the refractive index due to the heating of the sample by absorbed small fraction of the pump laser power. The change in the refractive index at this region imposes a nonlinear shift on the phase of the illuminating probe beam that leads to the Fresnel diffraction. Simulation and experimental studies show that the technique is reliable and quite sensitive to refractive index change.
27 citations
Posted Content•
TL;DR: Owing to the superior physical properties of the material, diamond CRLs could become indispensable wavefront-preserving primary focusing optics for X-ray free-electron lasers and the next-generation synchrotron storage rings.
Abstract: We report the fabrication and performance evaluation of single crystal diamond refractive x-ray lenses with a paraboloid of rotation form factor for focusing x-rays in two dimensions simultaneously. The lenses were manufactured using a femtosecond laser micromachining process and tested using x-ray synchrotron radiation. Such lenses were stacked together to form a standard compound refractive lens (CRL). Due to the superior physical properties of the material, diamond CRLs are enabling and indispensable wavefront-preserving primary focusing optics for x-ray free-electron lasers and the next-generation synchrotron storage rings. They can be used for highly efficient refocusing of the extremely bright x-ray sources for secondary optical schemes with limited aperture such as nanofocusing Fresnel zone plates and multilayer Laue lenses.
22 citations
TL;DR: The measured scintillation indices, and the correlation of the retro-reflected beam with the direct beam, are compared with a point source, point scatterer, and point receiver model in the strong scintilation approximation.
Abstract: Communications links that utilize modulating retro-reflectors can make use of turbulence-induced fade information available at the remote data-signal terminal in order to optimize the data transfer rate. Experiments were conducted to measure the irradiance in both the direct and the retro-reflected beams. Both on-axis and off-axis components were recorded in order to further study the enhancement in the scintillation index observed in the retro-reflected beam. Measurements were made over a 1.8 km terrestrial range at AP Hill, Virginia. The degree of correlation of the received irradiance between the direct and double-passage beams is found to approach 90% on-axis and 70% outside of the Fresnel zone radius. The scintillation index in the retro-reflected beam is enhanced on-axis due to reciprocal optical paths. The measured scintillation indices, and the correlation of the retro-reflected beam with the direct beam, are compared with a point source, point scatterer, and point receiver model in the strong scintillation approximation.
TL;DR: In this article, a photon sieve was used for de Broglie wave manipulation of ground-state helium atoms with an average wavelength of 0.055 nm, achieving a spot size of less than 4.5 nm.
Abstract: The manipulation of low-energy beams of neutral atoms and molecules via their de Broglie wavelength is a branch of atom optics often referred to as de Broglie matter wave optics. The application areas include fundamental quantum mechanics, atom interferometry, and the development of new microscopy instrumentation. The focusing of de Broglie matter waves with a Fresnel zone plate was used to demonstrate the first neutral helium microscopy imaging. The ultimate resolution of such a microscope is limited by the width of the outermost zone. Because a Fresnel zone plate for atoms cannot be fabricated on a substrate (the low-energy atom beams would not be able to penetrate the substrate material), this gives a fabrication determined limit for the first-order focus of around 30--50 nm. Therefore, it is important to search for alternative optical elements that enable higher resolution. Photon sieves consist of a large number of pinholes, arranged suitably relative to the Fresnel zones. The great advantages are that the width of the pinholes can be larger than the respective Fresnel zones and a free-standing pinhole is much easier to fabricate than a free-standing zone. Thus, with a photon-sieve structure applied for de Broglie matter wave manipulation, the fabrication limit for focusing is reduced to potentially around 3--5 nm. Here we present a realization of such an ``atom sieve,'' which we fabricated out of a silicon nitride (SiN) membrane, using electron-beam lithography and reactive ion etching. Our atom sieve is 178 $\ensuremath{\mu}\mathrm{m}$ in diameter and has 31 991 holes. The diameter of the holes varies from 1840 to 150 nm. Using a beam of neutral, ground-state helium atoms with an average wavelength of 0.055 nm, we demonstrate helium atom focusing down to a spot size of less than 4 $\ensuremath{\mu}\mathrm{m}$. The focus size is limited by the intrinsic velocity spread of the helium beam.
TL;DR: In this article, phase shifted linear Fresnel zone plates are presented for the first time, and the impact of the phase shifting on their diffractive and focusing properties are studied, and it is demonstrated that by shifting the phase, two parallel linear beams can be generated at the focal plane.
Abstract: Phase shifted linear Fresnel zone plates are presented for the first time. These diffractive elements are linear Fresnel zone plates in which their phase are laterally shifted. The impact of the phase shifting on their diffractive and focusing properties are studied. It is demonstrated that by shifting the phase, two parallel linear beams can be generated at the focal plane. Furthermore, as they are propagating, a non-diffractive line-shaped beam is generated at a given distance from the focus. Transverse intensity profile of the beam at different distances as well as its cross section of propagation along the optical axis clearly shows that the intensity profile of the beam is really kept unchanged as it is propagated. All results are completely verified by experiments.
TL;DR: In this article, a cross-like Fresnel zone plate was analyzed and the focusing properties of the element were compared to a classic and square Fresnel plate, and it was shown that the focusing of the elements is well corrected in comparison to square and rectangular Fresnel zones.
TL;DR: An implementation of the quasi-discrete Hankel transform where a partial transform matrix can be stored to speed up repeated wave propagations over specified distances, with reduced computational memory requirements is described.
Abstract: When calculating the focusing properties of cylindrically symmetric focusing optics, numerical wave propagation calculations can be carried out using the quasi-discrete Hankel transform (QDHT). We describe here an implementation of the QDHT where a partial transform matrix can be stored to speed up repeated wave propagations over specified distances, with reduced computational memory requirements. The accuracy of the approach is then verified by comparison with analytical results, over propagation distances with both small and large Fresnel numbers. We then demonstrate the utility of this approach for calculating the focusing properties of Fresnel zone plate optics that are commonly used for x-ray imaging applications and point to future applications of this approach.
17 May 2015
TL;DR: In this paper, photo-induced Fresnel zone plates (PI-FZPs) are formed by directly illuminating a high-resistivity silicon wafer with the desired patterns using a digital light processing (DLP) projector, without any circuit or device fabrication.
Abstract: We report a novel and simple approach to realize terahertz (THz) dynamic two-dimensional (2D) beam steering and forming antennas, based on reconfigurable photo-induced Fresnel zone plates (PI-FZPs). The FZPs are formed by directly illuminating a high-resistivity silicon wafer with the desired patterns using a digital light processing (DLP) projector, without any circuit or device fabrication. At 750 GHz, the THz beam from a diagonal horn antenna has been steered two dimensionally over a range from approximately −12° to +12° from the antenna boresight, by projecting different PI-FZP patterns. In addition, using PI-FZPs with different focal lengths, the THz beam size can be dynamically tuned. Both the beam steering and forming can be performed simultaneously without affecting the antenna performance, making this an enabling technology for emerging THz applications such as sensing, imaging, tracking, adaptive wireless communications and short-range high-speed interconnections.
01 Sep 2015
TL;DR: A versatile near-ground field prediction model is proposed to facilitate accurate WSN simulations and is validated against experimental data sets obtained in different scenarios.
Abstract: A versatile near-ground field prediction model is proposed to facilitate accurate WSN simulations. Path loss is split into three segments using the principles of the Fresnel zones. The distances that define the edges of each segment are derived theoretically. The model is validated against experimental data sets obtained in different scenarios. All the propagation features affecting the direct, reflected, and higher order scattered waves are effectively incorporated in the model. Effects of antenna height, frequency of operation, polarization, and terrain electrical and geometrical properties on the connectivity of low-altitude WSNs are studied through Monte Carlo simulations.
TL;DR: Detailed study of near-field and far-field visible light scattering from lithographically defined micron scale dielectric particles allows a previously un-obtainable level of control over the intensity distribution in the near- field, compared to spherically and cylindrically symmetric scattering particles.
Abstract: We experimentally and numerically study near-field and far-field visible light scattering from lithographically defined micron scale dielectric particles. We demonstrate field confinement and elongated intensity features known as photonic nanojets in the Fresnel zone. An experimental setup is introduced which allows simultaneous mapping of the angular properties of the scattering in the Fresnel zone and far-field regions. Precise control over the shape, size and position of the scatterers, allows direction control of the near-field intensity distribution. Intensity features with 1/3 the divergence of free space Gaussian beams of similar waist are experimentally observed. Additionally the direction and polarization of the incident light can be used to switch on and off intensity hot spots in the near-field. Together these parameters allow a previously un-obtainable level of control over the intensity distribution in the near-field, compared to spherically and cylindrically symmetric scattering particles.
TL;DR: Widespread simulation results are provided to compare the models based on theoretical rays in terms of prediction accuracy and computation time and different operation frequencies and transmitting antenna heights are considered by using a high-performance computing technique.
Abstract: The propagation of electromagnetic waves in empty space is an extremely simplified case. Thus, the significant question is how an electromagnetic wave propagates in an environment with obstacles such as buildings, trees or hills. Electromagnetic waves are partially reflected and partially diffracted from these obstacles. To predict the relative path loss of electromagnetic waves at the receiving position, many electromagnetic-wave propagation models have been proposed. These propagation models can be classified into models based on numerical integration and those based on ray tracing. Uniform theory of diffraction (UTD) and slope-UTD (S-UTD) models are ray-tracing-based propagation models and are briefly explained in this paper. In addition, detailed information is provided about the improved slope UTD model, which is called the S-UTD with Convex Hull (S-UTD-CH) model. The fundamentals of the S-UTD-CH model are the S-UTD, convex hull and Fresnel zone concept. In particular, the S-UTD-CH model can ...
TL;DR: In this paper, the authors developed a ray tracing simulation tool for imaging systems including a Fresnel lens with a quasi-arbitrary sidewall structure, where locally, a sidewall can freely be oriented.
Abstract: We developed a ray tracing simulation tool for imaging systems including a Fresnel lens with a quasi-arbitrary sidewall structure. One issue with Fresnel lens is that noise in the image plane can appear from rays passing through or reflected at its sidewalls. One way to reduce it is to modify the orientation of the sidewalls so that rays will not reach the image plane. To find the best sidewall orientations, we developed a method where locally, a sidewall can freely be oriented. We could then derive the best modulation scheme for each Fresnel lens sidewall. In the case of a single imaging Fresnel lens, relative parasite noise intensity could mostly be prevented. To experimentally check our method, snapshot images were taken with single Fresnel lenses and a single spherical lens. No noticeable differences in image quality could be observed using a standard C-MOS camera. However, parasite noise could experimentally be detected with a Fresnel lens prototype when using a very high-dynamic range C-MOS camera.
TL;DR: In this article, a binary composite diffractive optical element with the functions of a spiral phase plate (SPP), an axicon, and a Fresnel zone lens (FZL) were designed with different topological charges.
Abstract: Binary composite diffractive optical elements with the functions of a spiral phase plate (SPP), an axicon, and a Fresnel zone lens (FZL) were designed with different topological charges. The element was designed in two steps. In the first step, the function of an SPP was combined with that of an axicon by spiraling the periods of the axicon with respect to the phase of the SPP followed by a modulo- 2π phase addition with the phase of an FZL in the second step. The higher-order Bessel beams generated by the binary phase spiral axicon are superposed at the FZL’s focal plane. Although location of the focal plane is wavelength dependent, the radius of the flower-like beams generated by the element was found to be independent of wavelength. The element was fabricated using electron-beam direct writing. The evaluation results matched well with the simulation results, generating flower-like beams at the focal plane of the FZL.
TL;DR: In this paper, image plane holographic microscopy in the soft X-ray (SXR) spectral region was demonstrated, combining the coherent output from a 46.9-nm wavelength table-top SXR laser and two Fresnel zone plates.
Abstract: We demonstrate image plane holographic microscopy in the soft X-ray (SXR) spectral region, combining the coherent output from a 46.9-nm wavelength table-top SXR laser and two Fresnel zone plates. Phase and amplitude maps of the object are simultaneously obtained from holograms created at the image plane by the superposition of a reference and object beam originating from the zero and first diffraction order of the zone plates. We have used the microscope to record holograms of nanometer-scale periodic Si elbow patterns with 30% absorption contrast at the laser wavelength. The measured phase shift of 2.3 rad accurately predicts the Si dense line step height of 100 nm. The scheme is scalable to shorter wavelengths and allows for simultaneous high spatial and temporal resolution.
TL;DR: The aspect ratio limit in polymethyl methacrylate by electron-beam lithography under 100 keV should be extremely useful for guiding further technical development in nanofabrication of high-quality Fresnel zone plates.
Abstract: For acquiring high-contrast and high-brightness images in hard-x-ray optics, Fresnel zone plates with high aspect ratios (zone height/zone width) have been constantly pursued. However, knowledge of aspect ratio limits remains limited. This work explores the achievable aspect ratio limit in polymethyl methacrylate (PMMA) by electron-beam lithography (EBL) under 100 keV, and investigates the lithographic factors for this limitation. Both Monte Carlo simulation and EBL on thick PMMA are applied to investigate the profile evolution with exposure doses over 100 nm wide dense zones. A high-resolution scanning electron microscope at low acceleration mode for charging free is applied to characterize the resultant zone profiles. It was discovered for what we believe is the first time that the primary electron-beam spreading in PMMA and the proximity effect due to extra exposure from neighboring areas could be the major causes of limiting the aspect ratio. Using the optimized lithography condition, a 100 nm zone plate with aspect ratio of 15/1 was fabricated and its focusing property was characterized at the Shanghai Synchrotron Radiation Facility. The aspect ratio limit found in this work should be extremely useful for guiding further technical development in nanofabrication of high-quality Fresnel zone plates.
Patent•
29 Apr 2015
TL;DR: In this article, a near-surface tomographic velocity analysis method based on the Fresnel zone is proposed, which has the advantages of the physical geography significance, the stability is strong, the efficiency is high, and calculation results are more real and reliable.
Abstract: The invention discloses a near-surface tomographic velocity analysis method. The near-surface tomographic velocity analysis method comprises the following steps: picking up travel time of first arrival by aiming at pre-stack data, and obtaining an initial model reflecting underground medium velocity distribution by pre-stack processing; performing a shortest path ray tracing method on the model to obtain simulated travel time; performing wave field simulation on the model by utilizing a frequency domain wave equation to obtain a sensitive kernel function reflecting disturbance of a medium to the travel time; establishing a corresponding inversion equation and solving to obtain a slowness updating amount. According to the tomographic velocity analysis based on the Fresnel zone, the problem that the solution of a large-scale sparse matrix is instable during the traditional temographic velocity analysis based on the ray theory is solved, and the seismic wave propagation rule is more truly portrayed; the near-surface tomographic velocity analysis method has the advantages that the physical geography significance is obvious, the stability is strong, the efficiency is high, and calculation results are more real and reliable.
Patent•
21 Jan 2015
TL;DR: In this paper, a three-dimensional dip angle domain stationary phase pre-stack time migration method and system is presented, which comprises the steps that prestack seismic data are read, and a migration speed field and a stretching and removing parameter are determined; according to the migration speed fields and the stretching-and-removal parameters, two dip angle channel sets corresponding to dip angles in the directions parallel to and perpendicular to a measuring line respectively are generated through a selected imaging line; based on the two dip angles channel sets on the selected line, Fresnel zones in the selected imaging
Abstract: The invention discloses a three-dimensional dip angle domain stationary phase pre-stack time migration method and system. The method comprises the steps that pre-stack seismic data are read, and a migration speed field and a stretching and removing parameter are determined; according to the migration speed field and the stretching and removing parameter, two dip angle channel sets corresponding to dip angles in the directions parallel to and perpendicular to a measuring line respectively are generated through a selected imaging line; based on the two dip angle channel sets on the selected imaging line, Fresnel zones in the two dip angle directions are picked up, and the Fresnel zones of all imaging points on a quasi imaging block are obtained through interpolation; through the obtained Fresnel zones of all the imaging points, three-dimensional stationary phase pre-stack time migration is carried out, and migration results corresponding to different migration distances are obtained; the migration results of three-dimensional stationary phase pre-stack time migration are collected, and a three-dimensional imaging data body is formed; the three-dimensional imaging data body is converted into a profile image of an underground reflection structure. According to the method and system, the problem that when a high dip angle structure exists, the signal to noise ratio of the migration image obtained through an existing migration imaging technology is low is effectively solved.
TL;DR: In this article, the non-paraxial propagation behavior of Laguerre-Gaussian (LG) beams under the tight focusing condition was studied by using the Rayleigh-Sommerfeld integrals.
TL;DR: In this paper, the authors considered the X-ray interferometer consisting of three Fresnel zone plates with the same optical axis, which operates in the amplitude-division mode and does not impose the strong requirements on the coherence of initial radiation.
Abstract: The X-ray interferometer consisting of three Fresnel zone plates with the same optical axis is considered. The interferometer operates in the amplitude-division mode and does not impose the strong requirements on the coherence of initial radiation. The interferometer is the modification of earlier one, with the main difference that the labor-intensive to manufacture multilevel Fresnel zone plates are replaced by the ordinary bi-level ones. The longitudinally and transversely defocused modifications of interferometer were considered by the numerical simulation method.
Patent•
30 Nov 2015
TL;DR: In this article, a generalized phase contrast (GPC) system for non-monochromatic electromagnetic waves is presented, which includes a source (12) of electromagnetic waves, a phase modifying element (18) with an input surface (x, y) positioned so that the electromagnetic waves are incident upon it and configured for phase modulation of the electromagnetic signals impinging on the surface by phasor values e ϕ(λ, x, y).
Abstract: A new generalized phase contrast (GPC) system is provided that is designed for non-monochromatic electromagnetic waves, comprising • a source (12) of electromagnetic waves for emission of electromagnetic waves with a plurality of wavelengths A, • a phase modifying element (18) with an input surface (x, y) positioned so that the electromagnetic waves are incident upon it and configured for phase modulation of the electromagnetic waves impinging on the surface (x, y) by phasor values e i ϕ(λ, x, y) • first Fourier or Fresnel optics (29) positioned so that the phase modulated electromagnetic waves are incident upon it and configured for Fourier or Fresnel transforming the phase modulated electromagnetic waves, • a spatial phase filter (22) with a surface S positioned at the Fourier or Fresnel plane of the first Fourier or Fresnel optics, respectively, and having phase shifting regions (x s , y S ) configured for phase shifting Fourier or Fresnel transformed electromagnetic waves with different wavelengths A incident on the respective phase shifting regions (x s , y S ) by predetermined respective phase shift values 6(h, x s , y S ) with relation to the remaining part of the respective Fourier or Fresnel transformed electromagnetic waves incident on parts of the surface S without a phase shifting region, and second Fourier or Fresnel optics (26) configured for forming the intensity pattern I (A, x', y') by Fourier or Fresnel transforming the Fourier or Fresnel transformed electromagnetic waves.
TL;DR: In this paper, the EarthStudy 360 Imager attenuated different types of wave characteristics considered as both random and coherent noise, in particular, different orders of multiples, and non-reflection seismic events such as Rayleigh, refraction, diffraction and side waves.
Abstract: The EarthStudy 360 Imager is an advanced depth imaging system that first maps the full recorded seismic data into the subsurface grid points and then decomposes the data into local angle domain (LAD) bins. It is based on specially designed diffraction operators using bottom-up ray tracing. In this article, we focus on the ability of the EarthStudy 360 Imager to attenuate different types of wave characteristics considered as both random and coherent noise – in particular, different orders of multiples, and non-reflection seismic events such as Rayleigh, refraction, diffraction and ‘side’ waves. The method is based on internal implementation of local slant stack (LSS) operators optimally designed for each primary ray pair associated with a given source-image point-receiver path and the corresponding seismic data event. The LSS is applied in the direction of the horizontal slowness components of the arriving rays at the acquisition surface, where the size of the LSS (the number of traces involved) is computed independently for each ray pair from its first Fresnel zone. Thus, primary reflection events sharing the same traveltime and the same surface directivity as the traced ray pairs are emphasized (highly weighted), while all other events (considered as noise) are simultaneously attenuated. We demonstrate our method in four different land data examples with different levels of geological complexities.
TL;DR: In this paper, a femtosecond (320 fs) high repetition rate (100 kHz) Yb:KGW laser system was used together with high precision linear positioning stages.
Abstract: The goal of this study was to integrate Fresnel zone plates with diameters up to 300 μm in the bulk of sapphire crystal by direct laser writing technique. These zone plates are intended to be integrated directly into GaN LED substrate because of their potential to increase the light extraction efficiency of UV LED devices. For integration task a femtosecond (320 fs) high repetition rate (100 kHz) Yb:KGW laser system was used together with high precision linear positioning stages. By exposing sapphire to the focused femtosecond laser radiation, regions of modified refractive index were induced and required zone plates were patterned. The discussions about optimal fabrication parameters as well as focusing properties of fabricated zone plates are presented. It is shown that sapphire can be a suitable material for microphotonic device integration: working zone plates with diameters up to 300 μm and diffraction efficiencies up to 23% were integrated below (80 μm) the sapphire surface.