Showing papers on "Fresnel zone published in 2010"

Tutorial on seismic interferometry: Part 1 — Basic principles and applications

Abstract: Seismic interferometry involves the crosscorrelation of responses at different receivers to obtain the Green’s function between these receivers. For the simple situation of an impulsive plane wave propagating along the x-axis, the crosscorrelation of the responses at two receivers along the x-axis gives the Green’s function of the direct wave between these receivers. When the source function of the plane wave is a transientas in exploration seismology or a noise signalas in passive seismology, then the crosscorrelation gives the Green’s function, convolved with the autocorrelation of the source function. Direct-wave interferometry also holds for 2D and 3D situations, assuming the receivers are surrounded by a uniform distribution of sources. In this case, the main contributions to the retrieved direct wave between the receivers come from sources in Fresnel zones around stationary points. The main application of direct-wave interferometry is the retrieval of seismic surface-wave responses from ambient noise and the subsequent tomographic determination of the surfacewave velocity distribution of the subsurface. Seismic interferometry is not restricted to retrieving direct waves between receivers. In a classic paper, Claerbout shows that the autocorrelation of the transmission response of a layered medium gives the plane-wave reflection response of that medium. This is essentially 1D reflected-wave interferometry. Similarly, the crosscorrelation of the transmission responses, observed at two receivers, of an arbitrary inhomogeneous medium gives the 3D reflection response of that medium. One of the main applications of reflected-wave interferometry is retrieving the seismic reflection response from ambient noise and imaging of the reflectors in the subsurface. A common aspect of direct- and reflected-wave interferometry is that virtual sources are created at positions where there are only receivers without requiring knowledge of the subsurface medium parameters or of the positions of the actual sources.

Tunable-focus flat liquid-crystal diffractive lens.

Abstract: We demonstrate an innovative variable-focus flat liquid-crystal diffractive lens (LCDL) with 95% diffraction efficiency and millisecond switching times using a +/-2.4 V ac input. This lens is based on the electrical modulation of a 3 mum layer of nematic liquid-crystal sandwiched between a Fresnel zone electrode structure and a reference substrate. Each zone is divided into 12 subzones to digitize the phase profiles and define the phase wrapping points. The focusing power can rapidly be switched by electrically changing the number of subzones and re-establishing the wrapping points. Potential applications include zooms with no moving parts and autofocus lenses for compact imaging devices.

Sub-70 nm resolution tabletop microscopy at 13.8 nm using a compact laser–plasma EUV source

Abstract: We report the first (to our knowledge) demonstration of a tabletop, extreme UV (EUV) transmission microscope at 13.8nm wavelength with a spatial (half-pitch) resolution of 69nm. In the experiment, a compact laser–plasma EUV source based on a gas puff target is applied to illuminate an object. A multilayer ellipsoidal mirror is used to focus quasi-monochromatic EUV radiation onto the object, while a Fresnel zone plate objective forms the image. The experiment and the spatial resolution measurements, based on a knife-edge test, are described. The results might be useful for the realization of a compact high-resolution tabletop imaging systems for actinic defect characterization.

General astigmatic transform of Hermite-Laguerre-Gaussian beams

Abstract: The general astigmatic transform, or two-dimensional non-separable linear canonical transform of a Hermite-Laguerre-Gaussian beam, is investigated by theoretical means. Some corollaries that apply to Hermite-Gaussian and Laguerre-Gaussian beam propagation are presented and discussed.

Analysis of spectrum distribution and optical losses under Fresnel lenses

Abstract: During late 1970s and early 1980s, Fresnel lenses have received more attention in the field of solar energy application. This paper briefly examines the Fresnel lens development since 1970s and investigates the losses inherent in the linear Fresnel lenses. The research develops the formulation that helps to quantify the linear lens’ transmittance loss and prism-tip scattering loss and then derive a realistic model to simulate the measured data. In addition, the research has identified an elliptical-based lens that comes closest to the condition of minimum deviation. Such lens closely duplicates the curvature needed for maximum transmission. The researcher applies different design wavelengths to study the contribution of each wavelength interval on the receiving plane.

Multifractal zone plates.

Abstract: We present multifractal zone plates (MFZPs) as what is to our knowledge a new family of diffractive lenses whose structure is based on the combination of fractal zone plates (FZPs) of different orders. The typical result is a composite of two FZPs with the central one having a first-order focal length f surrounded by outer zones with a third-order focal length f. The focusing properties of different members of this family are examined and compared with conventional composite Fresnel zone plates. It is shown that MFZPs improve the axial resolution and also give better performance under polychromatic illumination.

Feasibility study of hard-x-ray nanofocusing above 20 keV using compound photon sieves

Abstract: Combining the advantages of photon sieves (PSs) and compound Fresnel zone plates (CZPs), we designed compound photon sieves (CPSs) for hard-x-ray nanofocusing. A CPS consists of an inner PS using the first-order diffraction surrounded by an outer zone plate using the third-order diffraction. A robust digital prolate spheroidal window was used as an apodization window for the inner PS, making CPSs more flexible than CZPs. CPSs can provide not only slightly better resolution compared to CZPs, but also it can significantly suppress the sidelobes, leading to a high signal-to-noise ratio. Further improvement of the high-aspect-ratio metal nanostructure process will allow CPSs to be a promising candidate for hard-x-ray nanofocusing in the high-energy region above 20keV.

Focusing properties of Fresnel zone plates with spiral phase

Abstract: Focusing properties of Fresnel zone plates with spiral phase with integer and fractional topological charges illuminated by plane wave are studied. Numerical results show that hollow beams can be generated and can also be controlled by the number of the zones and the topological charge, which implies the potential applications of such kind of zone plate in trapping and manipulating particles.

Square Fresnel zone plate with spiral phase for generating zero axial irradiance

Abstract: A type of square Fresnel zone plate with spiral phase for generating zero axial irradiance is proposed. Diffraction patterns of the zone plates with different generalized topological charges are given by numerical simulation, which also suggests their potential applications in generating hollow beams.

Thin microwave phase-shifting surface lens antenna made of square elements

Abstract: A 90° phase-correcting Fresnel zone plate (FZP) antenna has been realised at 30°GHz using a thin three-layer microwave phase-shifting surface (PSS) with square conducting shapes as the unit cell elements. These square elements allow dual-polarisation or circular-polarisation capabilities, which could not be achieved by the previously reported PSS structures the unit cell elements of which were strip-based. This new PSS lens was compared with the previously reported strip-element version. The square element PSS lens has slightly higher gain, but a small degradation to cross-polarisation level and gain bandwidth. The effect of altering the roll angle of the lens with the feed kept fixed was also investigated. This revealed that gain bandwidth is unchanged, but there is a marginal gain degradation and increase in the cross-polarisation level (albeit still well within an acceptable range) for certain roll angles.

Fresnel-zone binning: Fresnel-zone shape with offset and velocity function

Abstract: The concept of the Fresnel zone has been explored by many workers; most commonly, their work has involved examining the Fresnel zone in the limiting case of zero offset and constant velocity. I have examined the shape of the Fresnel zone for nonzero offset and in the situation of constant velocity gradient. Finite-offset Fresnel zones are not circular but are elliptical and may be many times larger than their zero-offset equivalents. My derivation takes a largely geometric approach, and I suggest a useful approximation for the dimension of the Fresnel zone parallel to the shot-receiver azimuth. The presence of a velocity gradient (velocity increasing with depth) in the subsurface leads to an expansion of the Fresnel zone to an area that is far larger than may be determined through a more usual straight-ray determination.

High efficiency multilevel phase-type Fresnel zone plates produced by two-photon polymerization of SU-8

Abstract: In this paper, we report on high quality two-level phase-type Fresnel zone plates (FZPs) produced by femtosecond laser two-photon polymerization of the resin SU-8. The optical focusing property was tested using a simple experimental setup. Moreover, the lens imaging functions 'JLU' and '' (English and Chinese abbreviations for Jilin University) were also demonstrated. In order to further enhance the diffraction efficiency, four-level and eight-level FZPs were designed using theoretical calculation and rapidly realized by point-to-point femtosecond laser scanning. In this way, the diffractive efficiency was enhanced from 35.8% for the two-level phase lens to 67% for the four-level phase lens and 73.9% for the eight-level phase lens, which are the largest values reported so far.

Improvements on Slope Diffraction for Multiple Wedges

Abstract: This article proposes an improved slope uniform theory of diffraction model for fast and more accurate field prediction for multiple wedge diffractions in the transition zone. The proposed method is based on the slope uniform theory of diffraction and the Fresnel zone concept, called the slope uniform theory of diffraction with convex hull. The article also provides simulation results for the comparison of the uniform theory of diffraction based algorithms with respect to the computation time and accuracy.

Lighting system and fresnel lens

Abstract: PROBLEM TO BE SOLVED: To provide a lighting system in which the light emitted to the side direction from a light source is utilized effectively, and most of light entered into an incident surface of a reflective system Fresnel lens is made to enter into a reflecting surface so as to utilize the light effectively. SOLUTION: The Fresnel lens 30 of a lighting system 1 has a refracted type Fresnel lens portion 41 and a reflected type Fresnel lens portion 51. The positions of second valley lines 57 of the reflected type Fresnel lens 51, in a direction along the optical axis Ax, are separated from the light source 20 or are mutually aligned, as the second valley lines 57 are arranged toward the outside. The distance in the direction along the optical axis from a second ridge line 56 to the second valley line 57 at the adjoining outside of the reflected type Fresnel lens 51 becomes larger as the second ridge line 56 is arranged farther outside. The reflecting surface 52 and the incident surface 53 at the outermost of the reflection-type Fresnel lens 51 surround the light source 20 along the circumference direction around the optical axis Ax. COPYRIGHT: (C)2011,JPO&INPIT

Rapid fabrication of an electrically switchable liquid crystal Fresnel zone lens.

Abstract: Based on a nanoimprint technique, a new method is proposed for the rapid fabrication of an electrically switchable liquid crystal Fresnel zone lens (SLCFZL). The flow chart of the proposed fabrication method for a SLCFZL is given and a binary SLCFZL is experimentally demonstrated using the proposed method. The diffraction efficiency of the SLCFZL is continuously tunable through an external electric field, and the driving voltage is relatively low (<15Vrms). The measured maximal diffraction efficiency reaches ∼35% for a linearly polarized light, which is close to the theoretical value of 40.5%. The focusing and imaging properties of the SLCFZL are also experimentally tested.

Compound Diffractive Lens Consisting of Fresnel Zone Plate and Frequency Selective Screen

Abstract: We describe a new Fresnel zone plate (FZP) and frequency selective screen (FSS) compound lens consisting of a binary FZP and FSS. The FZP has eight circular zones totally, four open and four closed, and the FSS is a square array of 40 × 40 four-leg loaded elements cut in a thin metal sheet. The FZP-FSS lens is designed for a paraxial plane-wave illumination at the frequency of 12 GHz, with a focal length of 15 cm. The compound lens is simulated and analyzed numerically by means of a specially developed hybrid PSTD-FDTD algorithm and software. The PSTD-FDTD results are contrasted with those obtained by lens prototype measurements. As a result, some attractive focusing and spectral properties of the FZP-FSS lens compared to the same-size FZP lens have been found: a frequency filtering property enhancement, about 2 dB increase in the peak focusing intensity, and more than 4 dB reduction of the first off-axis maximum. Both lenses have roughly the same transverse angular resolution.

Evaluation of the dynamic range and spatial resolution of nonadiabatic optical near-field lithography through fabrication of Fresnel zone plates

Abstract: Fresnel zone plates (FZPs) were fabricated in order to evaluate the performance of nonadiabatic photolithography by exploiting the localized nature of optical near fields. This novel photolithography scheme could realize FZPs with structures smaller than the wavelength of the light source used for exposure. The FZP for 325-nm-wavelength UV light could focus the incident light to a spot size of 590 nm. An FZP for focusing soft X-rays was also fabricated and, compared to conventional adiabatic photolithography, showed higher-contrast zones over the whole area of the FZP. This method exhibits a high dynamic range and good spatial resolution, and it was free from artifacts due to the interference of the residual propagating exposure light transmitted through the aperture of the photomask.

Scattering of Electromagnetic Waves From a Rectangular Plate Using an Enhanced Stationary Phase Method Approximation

Abstract: A time-efficient high frequency analytical model for the calculation of the scattered field from a perfect electric conductor (PEC) plate is presented here, which is based on the physical optics (PO) approximation and the stationary phase method (SPM). Using the SPM analysis for the three-dimensional (3D) scattering problem under consideration, the scattered electric field is calculated analytically. It follows that the analytical formula proposed here yields an accurate and fast algorithm for the calculation of the scattered electromagnetic (EM) field, which can be used trustfully in a variety of radio propagation problems. The accuracy of the proposed analytical method is checked through a straightforward numerical integration over the PO currents, as well as through finite element boundary integral full-wave exact solution. Comparison results are given in the far field, Fresnel zone and the near field area.

New type of x-ray source for lensless laboratory nano-CT with 50-nm resolution

Abstract: Most X-ray systems are limited in spatial resolution by the x-ray source performance. In laboratory sources, x-rays are generated by the interaction of an electron beam with a metal target. Bulk target sources produce a spot size in the micron range. Thin layer targets allow a spot size improvement down to hundreds of nanometers, but with a significant flux reduction. Until now a spatial resolution under 100 nm could only be achieved by imaging with Fresnel zone plates with limited depth of focus, typically - several microns. This is acceptable for imaging of flat objects, but it creates a problem for tomography, which requires all parts of a bulk object to be in focus. To overcome the limitations, we invented an x-ray source with a new type of target. Because x-ray cameras can only collect photons from a small angle, the new emitter is physically shaped in such way that the camera can see it as a small dot, but it has a big length along the direction perpendicular to the camera creating a significant flux without compromising the resolution. Evaluation shows that structures down to 50 nm can be distinguished while maintaining a significant x-ray flux and infinite depth of focus required for nano-tomographical reconstruction.

Partially coherent off-axis Gaussian beam scintillations

Abstract: The scintillation index at the receiver origin is formulated for a partially coherent off-axis Gaussian beam in atmospheric turbulence by employing the extended Huygens–Fresnel principle. Our formula correctly reduces to the existing coherent and partially coherent Gaussian beam scintillation indices in the limiting cases. For off-axis Gaussian beams with imaginary, real and complex displacement parameters, the scintillation index reduces when the incidence becomes more incoherent. When the source size of the off-axis Gaussian beam increases, the scintillations increase for partially coherent sources and decrease for incoherent sources, the tendency being observed for imaginary, real and complex displacement parameters. For the fully coherent off-axis Gaussian beams, increase in the source size first causes an increase in the scintillations, eventually reaching saturation at large source sizes, the increase is not monotonic and may exhibit a peak around the Fresnel zone sized off-axis Gaussian sources. Fo...

One‐Micron Beams for Macromolecular Crystallography at GM/CA‐CAT

Abstract: GM/CA‐CAT has developed a 1‐μm beam for challenging micro‐diffraction experiments with macromolecular crystals (e.g. small crystals) and for radiation damage studies. Reflective (Kirkpatrick‐Baez mirrors) and diffractive (Fresnel zone plates) optics have been used to focus the beam. Both cases are constrained by the need to maintain a small beam convergence. Using two different zone plates, 1.0×1.0 and 0.8×0.9 μm2 (V×H,FWHM) beams were created at 15.2 keV and 18.5 keV, respectively. Additionally, by introducing a vertical focusing mirror upstream of the zone plate, a line focus at 15.2 keV was created (28×1.4 μm2 V×H,FWHM) with the line oriented perpendicular to the X‐ray polarization and the crystal rotation axis. Crystal‐mounting stages with nanometer resolution have been assembled to profile these beams and to perform diffraction experiments.

Imaging properties of Fresnel zone plate-like surface plasmon polariton launching lenses

Abstract: A general design method of Fresnel zone plate-like surface plasmon polariton launching lenses (SPPLLs) with an arbitrary phase correction step is proposed, which can implement imaging between the far-field light and surface plasmon polaritons (SPPs). The imaging properties of half-wave SPPLLs, including the resolution power, object-image relationships, and aberrations, are investigated by using a simulation method based on Huygens-Fresnel principle with SPP point source model. The results show that SPPLLs are suitable for the connection between plasmonic and conventional diffraction-limited photonic devices.

Finite element modeling of acoustic field of physiotherapy ultrasonic transducers and the comparison with measurements

Abstract: This paper presents the modeling of the acoustic field of a physiotherapy ultrasonic transducer by using the finite element method. An ideal emission is presented obtained by using the approach developed by Rayleigh, called “piston in a baffle”. Simulations with FEM also are presented to compare them with the analytical results. The results of the model are also compared to those of the measurements in a physiotherapy transducer. The results show the efficacy of modeling the real transducers with ideal models in relation to the overlapping in the Fresnel zone and the characteristic parameters. A necessity is evident after this analysis: more appropriated models using more real boundary conditions. Results indicate that Fresnel zone is not correctly modeled using the ideal considerations.

Fabrication of X-ray imaging zone plates by e-beam and X-ray lithography

Abstract: X-ray imaging and microscopy techniques have been developed in worldwide due to their capabilities of large penetration power and high spatial resolution. Fresnel zone plates is considered to be one of the most convenient optic devices for X-ray imaging and microscopy system. The zone plates with aspect ratio of 7 and 13 have been fabricated by e-beam lithography combined with X-ray lithography in this paper. Firstly, the X-ray lithography mask of zone plates with outermost zone width of 100 nm was fabricated by e-beam lithography and gold electroplating techniques. Secondly, the zone plates with gold profile thickness of 700 and 1,300 nm were replicated by X-ray lithography and gold electroplating techniques. X-ray imaging and microscopy techniques were introduced to characterize the high-aspect-ratio zone plates’ inner structures. At the X-ray energy of 7.5 keV, the first-order focusing efficiency of zone plates with gold profile thickness of 700 nm is about 8.63%.

Cesrta x-ray beam size monitor operation

Abstract: We report on the design and operation of the CesrTA xray beam size monitor (xBSM). The xBSM resolution must be sufficient to measure vertical beam sizes of order 10um by imaging 2-4keV synchrotron radiation photons onto a one-dimensional photodiode array. Instrumentation in the evacuated x-ray beam line includes upstream interchangeable optics elements (slits, coded apertures, and Fresnel zone plates), a monochromator and an InGaAs photodiode detector. The readout is a beamsynchronized FADC that is capable of parallel measurement of consecutive bunches with 4ns spacing. The xBSM has been used to measure beam sizes during the August 2009, November 2009, and April 2010 runs. Single turn measurements are fit to characteristic image shapes to extract beam sizes independent of position variations. The turn-averaged beam size provides feedback for low-emittance tuning.