Showing papers on "Fresnel zone published in 2006"
TL;DR: The results show that for flat-topped Gaussian beams scintillation is larger than that of the single Gaussian beam scintillations when the source sizes are much smaller than the Fresnel zone.
Abstract: The scintillation index is formulated for a flat-topped Gaussian beam source in atmospheric turbulence. The variations of the on-axis scintillations at the receiver plane are evaluated versus the link length, the size of the flat-topped Gaussian source, and the wavelength at selected flatness scales. The existing source model that represents the flat-topped Gaussian source as the superposition of Gaussian beams is employed. In the limiting case our solution correctly matches with the known Gaussian beam scintillation index. Our results show that for flat-topped Gaussian beams scintillation is larger than that of the single Gaussian beam scintillation when the source sizes are much smaller than the Fresnel zone. However, this trend is reversed and scintillations become smaller than the Gaussian beam scintillations for flat-topped sources with sizes much larger than the Fresnel zone.
136 citations
TL;DR: It is shown that for a beam with a small degree of ellipticity and even order of singularity, two isolated intensity zeroes appear in the Fresnel zone on a straight line at an angle of 45 deg or -45 deg, depending whether the beam's spin is right or left.
Abstract: An analytical expression for the diffraction of an elliptic Laguerre-Gaussian (LG) beam is derived and analyzed. We show that a beam with even singularity order has nonzero axial intensity for any degree of ellipticity and at any finite distance z from the initial plane, whereas at z=0 and z=∞ the axial intensity is zero. We show that for a beam with a small degree of ellipticity and even order of singularity, two isolated intensity zeroes appear in the Fresnel zone on a straight line at an angle of 45 deg or −45 deg, depending whether the beam's spin is right or left. The theoretical conclusions are confirmed by numerical simulation and physical experiments.
78 citations
TL;DR: In this paper, the authors compared surface wave tomography models obtained using finite-frequency kernels and ray theory, and systematically changed regularization in both cases and plotted data misfit against the number of independent parameters in the solution.
Abstract: SUMMARY We compared surface wave tomography models obtained using finite-frequency kernels and ray theory. We systematically changed regularization in both cases and plotted data misfit against the number of independent parameters in the solution. Our tests show that models from finite-frequency kernels and ray-theoretical kernels are statistically similar. This means that any model obtained using one forward theory can be obtained using the other one by appropriately changing the damping constant. It is clear that finite-frequency theory is a better forward theory to represent the wavefield, but the associated inverse problem is not less ill posed. Indeed, current data coverage is such that the solution is dominated by the chosen regularization. This prevents us from achieving a resolution of the order of the Fresnel zone, or beyond, and noticing the benefits of a better forward theory.
77 citations
TL;DR: In this paper, the smallest spot size that hard x rays can be focused to using Fresnel zone plates was investigated and a large numerical aperture was used to focus hard x-rays down to below the theoretical limit.
Abstract: The question is addressed of what is the smallest spot size that hard x rays can be focused to using Fresnel zone plates. A thick tilted zone plate optic with large numerical aperture is considered in numerical simulations and is shown to efficiently focus hard x rays down to below $1\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, well below the theoretical limit for reflective optics such as waveguides and that of refractive optics. The focal spot size is ultimately limited by the atomic structure of matter. The practical realization of these optics will require a significant technological effort, but would enable hard x-ray nanoprobe studies with close to atomic resolution at current and future x-ray sources, such as x-ray free electron lasers and energy recovery linacs.
75 citations
TL;DR: The results demonstrate the feasibility of using focused soft x-ray laser beams for the direct nanoscale patterning of materials and the development of new nanoprobes.
Abstract: Ablation of holes with diameters as small as 82 nm and very clean walls was obtained in poly(methyl methacrylate) focusing pulses from a Ne-like Ar 46.9 nm compact capillary-discharge laser with a freestanding Fresnel zone plate diffracting into third order. These results demonstrate the feasibility of using focused soft x-ray laser beams for the direct nanoscale patterning of materials and the development of new nanoprobes.
59 citations
TL;DR: In this article, the authors consider the imaging of a point object into the first diffraction order of a volume zone plate having its zones parallel to the optical axis and find that the image has a minimal spot size approximately equal to the outermost zone width.
Abstract: The x-ray focusing properties of linear Fresnel zone plates have been derived by solving the Helmholtz equation for the field propagating through the zones. We consider the imaging of a point object into the first diffraction order of a volume zone plate having its zones parallel to the optical axis. For plane wave illumination, the focal spot size is limited by the same material-dependent but wavelength-independent value that affects waveguide focusing. In marked contrast, for the one-to-one imaging condition, corresponding to specular reflection of the x rays from the zone boundaries, the image is found to have a minimal spot size approximately equal to the outermost zone width. Unlike x-ray waveguides, zone plates therefore do not appear to possess a fundamental limit to the smallest spot size to which they can focus.
54 citations
TL;DR: In this article, the authors describe a sub-50nm resolution XCT system operating at 8 keV in absorption and Zernike phase contrast mode based on a commercially available laboratory x-ray source.
Abstract: X-ray computed tomography (XCT) is a powerful nondestructive 3D imaging technique, which enables the visualization of the three dimensional structure of complex, optically opaque samples. High resolution XCT using Fresnel zone plate lenses has been confined in the past to synchrotron radiation centers due to the need for a bright and intense source of x-rays. This confinement severely limits the availability and accessibility of x-ray microscopes and the wide proliferation of this methodology. We are describing a sub-50nm resolution XCT system operating at 8 keV in absorption and Zernike phase contrast mode based on a commercially available laboratory x-ray source. The system utilizes high-efficiency Fresnel zone plates with an outermost zone width of 35 nm and 700 nm structure height resulting in a current spatial resolution better than 50 nm. In addition to the technical description of the system and specifications, we present application examples in the semiconductor field.
50 citations
TL;DR: A modified version of a scanning holography microscope in which the Fresnel Zone Plates are created by a homodyne rather than a heterodyne interferometer, so the projected pattern on the specimen is frozen rather than varied as previously.
Abstract: We have developed a modified version of a scanning holography microscope in which the Fresnel Zone Plates (FZP) are created by a homodyne rather than a heterodyne interferometer. Therefore, during the scanning the projected pattern on the specimen is frozen rather than varied as previously. In each scanning period the system produces an on-axis Fresnel hologram. The twin image problem is solved by a linear combination of at least three holograms taken with three FZPs with different phase values.
48 citations
TL;DR: The high speed switching of the ferroelectric device together with recent advances in computer technology enable fast, smooth movement of traps that can be independently controlled in real time by the trapping and manipulation of yeast cells and fungal spores.
Abstract: A ferroelectric liquid crystal spatial light modulator is used to generate up to 24 independently controllable traps in a holographic optical tweezers system using time-multiplexed Fresnel zone plates. For use in biological applications, helical zone plates are used to generate Laguerre-Gaussian laser modes. The high speed switching of the ferroelectric device together with recent advances in computer technology enable fast, smooth movement of traps that can be independently controlled in real time. This is demonstrated by the trapping and manipulation of yeast cells and fungal spores.
41 citations
TL;DR: A scattering-free, polarization controllable Fresnel zone plate lens is demonstrated using a photo-induced alignment of the dye-doped liquid crystal film to provide orthogonal polarization states for odd and even zones.
Abstract: A scattering-free, polarization controllable Fresnel zone plate lens is demonstrated using a photo-induced alignment of the dye-doped liquid crystal film. This photo-aligned liquid crystal zone plate provides orthogonal polarization states for odd and even zones. The different focus orders can be separated because of their different polarization states. The fabrication process is relatively simple and the operation voltage is less than 5 Vrms.
38 citations
Patent•
18 Apr 2006TL;DR: In this paper, a Fresnel zone plate having a complex irradiation function capable of improving resolution even when the outermost opaque band width cannot be reduced and an X-ray microscope using the Fresnel plate was presented.
Abstract: [Object] To provide a Fresnel zone plate having a complex irradiation function capable of improving resolution even when the outermost opaque band width cannot be reduced and an X-ray microscope using the Fresnel zone plate. [Solution] A Fresnel zone plate 1 having a complex irradiation function according to the present invention has opaque bands 3 and transparent bands 4 arranged alternately in the radial direction from the center on a flat transparent substrate 2 , and a transmission window 7 formed such that a portion of a plane wave vertically applied onto the upper surface vertically enters directly a sample 6 disposed below the Fresnel zone plate 1.
TL;DR: A numerical method for calculation of the electromagnetic field in two-dimensionally confined x-ray waveguides is presented, based on the parabolic wave equation, which is solved by means of a finite-difference scheme.
Abstract: A numerical method for calculation of the electromagnetic field in two-dimensionally confined x-ray waveguides is presented. It is based on the parabolic wave equation, which is solved by means of a finite-difference scheme. The results are verified by a comparison to analytical theory, namely, Fresnel reflectivity and the weakly guiding optical fiber.
TL;DR: The design, testing and operation of a system for telecentric 3-dimensional imaging of dynamic objects is presented and application to studies of dynamic processes in microscopy is considered.
Abstract: The design, testing and operation of a system for telecentric imaging of dynamic objects is presented. The simple system is capable of rapid electronic scanning of a single focal plane within a specimen or of simultaneous focusing on multiple planes whose depth and relative spacing within the specimen can be changed electronically. Application to studies of dynamic processes in microscopy is considered.
TL;DR: In this article, the effect of changing the reference phase from the standard 0deg to any value between 0deg and 180deg was studied using finite difference time domain software to simulate a circular Fresnel zone plate antenna, and it was found that a significant improvement in the level of the first sidelobe could be achieved without sacrificing gain or cross-polarization levels.
Abstract: A circular Fresnel zone plate antenna was simulated using a finite difference time domain software to study the effect of changing the reference phase from the standard 0deg to any value between 0deg and 180deg. Several prototypes were built to validate the simulations using four different focal-length-to-diameter (F/D) ratios. It was found that a significant improvement in the level of the first sidelobe, up to about 9 dB according to the simulations, could be achieved without sacrificing gain or cross-polarization levels
TL;DR: Zernike phase contrast has been added to a full‐field X‐ray microscope with Fresnel zone plates that was in operation at 6.95 keV and a Halo effect coming from the Zernikephase contrast was clearly visible on the images of meshes.
Abstract: Zernike phase contrast has been added to a full-field X-ray microscope with Fresnel zone plates that was in operation at 6.95 keV. The spatial resolution has also been improved by increasing the magnification of the microscope objective looking at the CsI(Tl) scintillation crystal. Cu no. 2000 meshes and a zone plate have been imaged to see the contrast as well as the spatial resolution. A Halo effect coming from the Zernike phase contrast was clearly visible on the images of meshes.
TL;DR: In this paper, the theory of normal-incidence rays is generalized to accommodate P-and S-waves in layered isotropic and anisotropic media, and the calculation of the three main factors contributing to the two-way amplitude is formulated as a recursive process in the upward direction of the normal-inception rays.
Abstract: Inspired by recent ray-theoretical developments, the theory of normal-incidence rays is generalized to accommodate P- and S-waves in layered isotropic and anisotropic media. The calculation of the three main factors contributing to the two-way amplitude — i.e., geometric spreading, phase shift from caustics, and accumulated reflection/transmission coefficients — is formulated as a recursive process in the upward direction of the normal-incidence rays. This step-by-step approach makes it possible to implement zero-offset amplitude modeling as an efficient one-way wavefront construction process. For the purpose of upward dynamic ray tracing, the one-way eigensolution matrix is introduced, having as minors the paraxial ray-tracing matrices for the wavefronts of two hypothetical waves, referred to by Hubral as the normal-incidence point (NIP) wave and the normal wave. Dynamic ray tracing expressed in terms of the one-way eigensolution matrix has two advantages: The formulas for geometric spreading, phase shif...
TL;DR: Two examples are presented to illustrate the advantages of polarization coded apertures, in which the incoming light will rotate its polarization at a portion of an aperture.
Abstract: Two examples are presented to illustrate the advantages of polarization coded apertures, in which the incoming light will rotate its polarization at a portion of an aperture. In the first example the depth of field of a diffraction limited lens is increased without sacrificing the light throughput; in the second example the axial focal intensity of a pixelated Fresnel zone plate is increased by 100%. Both examples work for linearly polarized or unpolarized illumination.
TL;DR: In this paper, the design of plane Fresnel zone plates and binary-staircase kinoforms was analyzed for a non-imaging application aimed to increase the performance of point-like detectors.
01 Jan 2006
TL;DR: In this paper, the authors describe a sub-50nm resolution nanoCT system operating at 8 keV in Zernike phase contrast mode based on a commercially available laboratory x-ray source.
Abstract: X-ray computed tomography (CT) is a powerful nondestructive 3D imaging technique, which enables the visualization of the three dimensional internal structure of opaque materials such as semiconductor devices. Reports of high resolution CT research on life science, materials and semiconductor has mainly been confined to synchrotron radiation centers. This severely limits the availability and accessibility of x-ray microscopes and the wide proliferation of this methodology. We describe a sub-50nm resolution nanoCT system operating at 8 keV in Zernike phase contrast mode based on a commercially available laboratory x-ray source. The system utilizes high-efficiency Fresnel zone plates with an outermost zone width of 35nm resulting in spatial resolution better than 50 nm. The technical description of the system and failure analysis applications notably in visualizing voids, residues in metal interconnects, and competitive analysis in semiconductor devices will be discussed.
TL;DR: The intensity correlation of the modified speckle as a function of the grating displacement is obtained and compared with experimental results, and the possibilities of metrological applications in optical encoders are suggested.
Abstract: We present a study of the variations of a speckle pattern passing through a grating that can be displaced. This study is described theoretically by a simple model based on the scalar diffraction theory in the Fresnel zone. The intensity correlation of the modified speckle as a function of the grating displacement is obtained and compared with experimental results. The possibilities of metrological applications in optical encoders are suggested.
Patent•
13 Feb 2006
TL;DR: In this paper, a diffuser with spatially varying diffusing angles is used to compensate for the absence of the light collimation provided by the Fresnel lens, and the diffuser contains elliptical microstructures so that the diffusing cones in orthogonal directions are different.
Abstract: A Fresnel lens of the prior art is split into two Fresnel lenses to allow easier control of the horizontal and vertical viewing angles. In a second embodiment, the Fresnel lens is entirely eliminated. Instead, the diffuser contains elliptical microstructures so that the diffusing cones in orthogonal directions are different, eliminating the need for a Fresnel lens to perform this function. To compensate for the absence of the light collimation provided by the Fresnel lens, a diffuser with spatially varying diffusing angles is used.
TL;DR: In this article, an array of overlapping single-zone hexagonal Fresnel zone plate lens antennas was designed and tested at 30 GHz and a significantly lower overall profile can be achieved compared to a single lens of equivalent diameter.
Abstract: An array of overlapping single-zone hexagonal Fresnel zone plate lens antennas was designed and tested at 30 GHz. By arraying smaller-diameter lenses, a significantly lower overall profile can be achieved compared to a single lens of equivalent diameter. These arrays can also find use in spatial power combining or in imaging applications.
26 Jan 2006
TL;DR: In this paper, a theoretical approach based on the paraxial wave equation and the Fresnel integral is presented to investigate nonlinear hot-image formation of an intense laser beam, showing that these two images should be equally taken into account for large lasers optimization of system design.
Abstract: A theoretical approach, based on the paraxial wave equation and the Fresnel integral, are presented to investigate nonlinear hot-image formation of an intense laser beam. Fresnel-zone-plate-like hologram induced by the sum of a wave scattered from a small scatterer and a background wave produces the negative first order diffracted wave (conjugative wave) that is focused to an traditional hot-image, and the negative second order diffracted wave that develops to an intense second-order hot-image. It is seen by the analytical results that the two images may attain a high intensity level enough to damage optical components in high-power lasers, showing that these two images should be equally taken into account for large lasers optimization of system design.
TL;DR: In this article, the pulse envelope of an ultrashort pulsed beam is evaluated on the focal points of a Fresnel zone plate and the description of the field dynamics is given in terms of a diffraction-induced pulse train.
Abstract: The pulse envelope of an ultrashort pulsed beam is evaluated on the focal points of a Fresnel zone plate. The description of the field dynamics is given in terms of a diffraction-induced pulse train. Within these terms we follow an analytical procedure to characterize the temporal broadening observed at the principal focus, which is significant if the number of Fresnel zones exceeds the number of cycles in the pulse. For Gaussian-type envelopes, the focal field may be accurately expressed in a simple closed form. This expression has a flat-top shape at the principal focus and other odd-order foci, and a two-peak envelope in the case of a low-integer even-order focus. Finally, extremely high orders present a time-domain evolution that emulates a train of uniform pulses with temporal characteristics equivalent to those of the incident beam.
TL;DR: In this paper, the diffraction efficiencies of a Fresnel zone plate (ZP), fabricated by Xradia Inc. using the electron-beam writing technique, were measured using polarized, monochromatic synchrotron radiation in the extreme ultraviolet wavelength range 3.4-22 nm.
Abstract: The diffraction efficiencies of a Fresnel zone plate (ZP), fabricated by Xradia Inc. using the electron-beam writing technique, were measured using polarized, monochromatic synchrotron radiation in the extreme ultraviolet wavelength range 3.4-22 nm. The ZP had 2 mm diameter, 3330 zones, 150 nm outer zone width, and a 1 mm central occulter. The ZP was supported by a 100 nm thick Si 3 N 4 membrane. The diffraction patterns were recorded by CMOS imagers with phosphor coatings and with 5.2 μm or 48 μm pixels. The focused +n orders (n=1-4), the diverging -1 order, and the undiffracted 0 order were observed as functions of wavelength and off-axis tilt angle. Sub-pixel focusing of the +n orders was achieved. The measured efficiency in the +1 order was in the 5% to 30% range with the phase-shift enhanced efficiency occurring at 8.3 nm where the gold bars are partially transmitting. The +2 and higher order efficiencies were much lower than the +1 order efficiency. The efficiencies were constant when the zone plate was tilted by angles up to ±1° from the incident radiation beam. This work indicates the feasibility and benefits of using zone plates to measure the absolute EUV spectral emissions from solar and laboratory sources: relatively high EUV efficiency in the focused +1 order, good out-of-band rejection resulting from the low higher-order efficiencies and the ZP focusing properties, insensitivity to (unfocused) visible light scattered by the ZP, flat response with off-axis angle, and insensitivity to the polarization of the radiation based on the ZP circular symmetry. EUV sensors with Fresnel zone plates potentially have many advantages over existing sensors intended to accurately measure absolute EUV emission levels, such as those implemented on the GOES N-P satellites that use transmission gratings which have off-axis sensitivity variations and poor out-of-band EUV and visible light rejection, and other solar and laboratory sensors using reflection gratings which are subject to response variations caused by surface contamination and oxidation.
Proceedings Article•
01 Jul 2006TL;DR: In this paper, a hexagonal Fresnel zone plate antenna is introduced and compared to the traditional circular FZP antenna, and the comparison was carried out in simulation by using a finite-difference time-domain software.
Abstract: A novel hexagonal Fresnel zone plate antenna is introduced and compared to the traditional circular Fresnel zone plate antenna. The comparison was carried out in simulation by using a finite-difference time-domain software. Although the circular lens performs better, the hexagonal geometry is better suited for arrays and provides the ability to both improve the sidelobe level and shift the sidelobe location away from boresight. This is accomplished by appropriately rotating the rings that make up the lens and is achieved without sacrificing directivity or 3dB beamwidth.
TL;DR: In this article, the authors presented the first results using a very simple lift-off technique, which up to now allows the fabrication of FZP with sub-100nm resolution with 110nm metal rings.
TL;DR: It is shown that the foci intensities of 10 fs pulses are considerably lower than those of cw beams while the focal widths in the axial and radial directions are broadened and spectral modulation along the center of the diffraction patterns is indicated.
Abstract: Results of experimental and theoretical work performed to compare diffraction patterns and focal distributions of a Fresnel zone plate illuminated by ultrashort 10 fs pulsed and cw laser beams are presented. It is shown that the foci intensities of 10 fs pulses are considerably lower than those of cw beams while the focal widths in the axial and radial directions are broadened. Calculations also indicate the spectral modulation along the center of the diffraction patterns. These phenomena are explained by the coherent superposition of the composing frequency content.
TL;DR: The proposed expansions contain only elementary functions and permit all elementary operations; therefore no special functions or special algorithms are needed in the evaluation of either irradiance distributions or the integrated energy in a focused field.
Abstract: It is shown in an earlier paper dealing with flat-topped light beams [Opt. Lett.27, 1007 (2002)] that the profile of flat-topped beams can be expressed in the form 1−[1−exp(−xi2)]M, where xi is a dimensionless parameter and M is a nonnegative number. The expansion of the proposed expression is a finite series containing only the lowest-order Gaussian modes. This situation provides the possibility of reformulating the scalar theory of diffraction at an aperture in an opaque screen if the Gaussian mode expansion is employed to describe the boundary values of the light incident on the screen. As an example of this effort, an asymptotic model is established for three-dimensional irradiance distributions near the focus in systems of different Fresnel numbers. The proposed expansions contain only elementary functions and permit all elementary operations; therefore no special functions or special algorithms are needed in the evaluation of either irradiance distributions or the integrated energy in a focused field.
TL;DR: Experimental results of enhanced second- and third-harmonic generation efficiency from Fresnel-lensing effects are presented and are in good agreement with the results of a simple theoretical analysis.
Abstract: We present experimental results of enhanced second- and third-harmonic generation efficiency from Fresnel-lensing effects. We obtained enhancement by a factor of 6 in the third-harmonic yield by simply limiting the laser beam with an iris. Higher enhancement factors (up to 16) were obtained with a Fresnel zone plate. The experimental findings are in good agreement with the results of a simple theoretical analysis.