In-depth resolution from multifrequency Born fields scattered by a dielectric strip in the Fresnel zone

The achievable depth resolution in reconstructing the permittivity profile of a dielectric strip under the Born approximation when data are collected in the Fresnel zone is studied. We consider a rectilinear measurement aperture and an orthogonal and centered rectilinear investigation domain. The roles of the aperture extent and frequency diversity are highlighted.     

In-depth resolution for a strip source in the Fresnel zone

The problem of determining the achievable resolution limits in the reconstruction of a current distribution is considered. The analysis refers to the one-dimensional, scalar case of a rectilinear, bounded electric current distribution when data are collected by measurement of the radiated field over a finite rectilinear observation domain located in the Fresnel zone, orthogonal and centered with respect to the source. The investigation is carried out by means of analytical singular-value decomposition of the radiation operator connecting data and unknown, which is made possible by the introduction of suitable scalar products in both the unknown and data spaces. This strategy permits the use of the results concerning prolate spheroidal wave functions described by B. R. Frieden [Progress in Optics Vol. IX, E. Wolf, ed. (North-Holland, Amsterdam 1971), p. 311.] For values of the space-bandwidth product much larger than 1, the steplike behavior of the singular values reveals that the inverse problem is severely ill posed. This, in turn, makes it mandatory to use regularization to obtain a stable solution and suggests a regularization scheme based on a truncated singular-value decomposition. The task of determining the depth-resolving power is accomplished with resort to Rayleigh's criterion, and the effect of the geometrical parameters of the measurement configuration is also discussed.     

Sparsity-assisted phase retrieval in the Fresnel zone

We report simulation results on phase retrieval from single-shot Fresnel zone irradiance data. It is shown that a simplistic Gerchberg–Saxton (GS) type iterative approach fails to produce accurate phase recovery for this case. An image sparsity enhancement step added to the GS iteration is however seen to show excellent phase recovery. Discussion of sampling considerations is presented as this is an important point for achieving numerically accurate phase reconstructions. The implications of the simulation results for building a compact lens-less phase microscopy system are also described.     

用于OCT动态聚焦的液晶菲涅尔波带透镜研究

提出了利用液晶菲涅尔波带透镜实现光学相干层析成像(OCT)动态聚焦的方法.根据扭曲相液晶空间光调制器(TN-LCSLM)的光学特性,设计了适用于OCT动态聚焦的菲涅耳波带透镜.利用TN-LCSLM型菲涅耳波带透镜进行了变焦控制实验,焦距实测结果与设计值比较吻合.此外,本文讨论了采用TN-LCSLM型菲涅耳波带透镜实施动态聚焦涉及到的一些问题.     

Static and dynamic Fresnel zone lenses for optical interconnections

Abstract

Static and dynamic Fresnel zone lenses were fabricated in quartz glass by means of microstructuring techniques. Two types of on-axis and offaxis lenses with different focal lengths and of different apertures were designed to operate at wavelengths of 1·52 μm and 633 nm. The blazed profile of the onaxis and off-axis lenses was approximated by up to 16 and up to four discrete levels respectively. Dynamic, that is electrically switchable, lenses have been realized by filling the structured surface with liquid crystal. The optical properties of the lenses, such as the focal spot sizes and the diffraction efficiencies, were investigated. Further the switching behaviour of the dynamic lenses was studied. The design and fabrication of the static and dynamic, on-and off-axis Fresnel zone lenses as well as their optical and switching properties will be presented.     

Comprehensive focusing analysis of various Fresnel zone plates

A series-form expression for the individual diffracted field of a general annular ring is derived from the Rayleigh-Sommerfeld diffraction integral. It can be used for the accurate and fast simulation of any diffractive focusing element composed of concentric transparent rings. We present a comprehensive analysis, based on the leading term and the linear superposition principle, of the focusing performances of various Fresnel zone plates. Many problems, such as the equivalent aperture function, the diffraction efficiency, the focal spot pattern, the suppression of higher orders and the appearance of "fractional orders," and the explanation for the appearance of Fraunhofer diffraction patterns, are analytically investigated in detail. Because of the great similarity between Fresnel zone plates and multilevel diffractive lenses, most of the obtained results are also applicable to multilevel diffractive lenses.     

Enhanced Fresnel zone plate coded microscopy of large-size objects

A scheme for microscopy of relatively large-size objects by using Fresnel zone plate (FZP) coded imaging (FZ-PCI) is digitally demonstrated. The limit on the source size in zone-plate-based microscopy comes from interference of out-of-focus multidiffraction orders of the FZP with the focused-order image. From the study of the angular spectrum of the coded image, it is shown that noise contribution from higher orders to a lower-order image can be digitally suppressed by selective propagation of spatial frequencies. Similarly, noise from aliasing and noise from lower orders to a higher-order image can be reduced by spatially limiting the coded image. To my knowledge for the first time, the results of digitally performed FZPCI-based microscopy of an object that is three times larger than the first zone of the FZP with a resolution better than 2 microm are presented and discussed.     

原子层厚度菲涅尔波带片及其宽谱聚焦特性

基于菲涅尔波带片构型的平面衍射透镜在现代光学系统中发挥着重要的作用,是高端光学成像系统等应用的关键元器件之一.现有菲涅尔波带片结构多基于金属薄膜或高折射率电介质材料来制备,难以满足集成光电子系统可集成化的核心需求.本文提出一种基于原子层厚度二维材料的菲涅尔波带片结构,基于损耗辅助的相位调控机制,在原子层厚度的MoS2二...     

Computational study of diffraction patterns for near-field Fresnel and Gabor zone plates

Near-field designs of Fresnel and Gabor zone plates are computationally analyzed by using versions that allow the foci to be brought closer to the plate than in the usual far-field applications. It is found that the Fresnel plate has a dominant primary conjugate pair of foci well inside the far-field region and a more intense primary focus and smaller off-focal-plane sidelobes than the near-field Gabor systems, thus yielding a superior imaging performance.     

Fabrication and testing of sputtered-sliced kinoform style Fresnel zone plate

The Fresnel zone plate (FZP) is a type of lens for focusing X-rays. We have fabricated a kinoform style FZP with a 30-step structure composed of concentric multilayer of alternating Cu layer, Al layer, and 28 composite material (Cu, Al) layers. The multilayer was deposited using a magnetron sputtering apparatus with two DC-sputtering guns. The focusing characteristics were evaluated at the synchrotron radiation beamline of SPring-8, and the focused beam size measured by knife-edge scanning was 0.8 μm at 40 keV. The peak diffraction efficiencies measured using ion chambers for 1st- and 2nd-order diffraction were 42% and 12% at 40 keV and 20 keV, respectively. High-order X-ray diffraction was also examined using the data obtained from a CCD camera.     

Fabrication and testing of sputtered-sliced kinoform style Fresnel zone plate

The Fresnel zone plate (FZP) is a type of lens for focusing X-rays. We have fabricated a kinoform style FZP with a 30-step structure composed of concentric multilayer of alternating Cu layer, Al layer, and 28 composite material (Cu, Al) layers. The multilayer was deposited using a magnetron sputtering apparatus with two DC-sputtering guns. The focusing characteristics were evaluated at the synchrotron radiation beamline of SPring-8, and the focused beam size measured by knife-edge scanning was 0.8 μm at 40 keV. The peak diffraction efficiencies measured using ion chambers for 1st- and 2nd-order diffraction were 42% and 12% at 40 keV and 20 keV, respectively. High-order X-ray diffraction was also examined using the data obtained from a CCD camera.     

Modified Fresnel zone plates that produce sharp Gaussian focal spots

A modified Fresnel zone plate that can produce an approximate Gaussian focal spot is proposed for the focusing and imaging of soft x rays and extreme ultraviolet radiation. The selection conditions for the positions and the widths of the concentric open rings are analytically presented. The focal spot size can be much smaller than the width of the narrowest open ring, and the sidelobes and the higher orders can be effectively suppressed. Through numerical experiments, we confirm that a Gaussian focal spot with a beam width of 7.7 nm can be produced by a modified Fresnel zone plate with a minimum structure size of 30 nm.     

New approaches to fabrication of multilayer Fresnel zone plate for high-energy synchrotron radiation X-rays

A multilayer (sputtered-sliced) Fresnel zone plate (FZP) is one of the promising focusing optics with high spatial resolution for the high-energy X-ray region. This is because a large “aspect ratio” can be realized easily. In addition, it is important that the kinoform FZP (theoretical diffraction efficiency=100%) can be fabricated by the sputtered-sliced method. This paper presents the experimental results of two new approaches for fabrication of a multilayer FZP for X-rays. (1) To achieve higher diffraction efficiency, a multilevel-type (4-step: quasi-kinoform type) FZP was fabricated. This FZP was composed of concentric multilayers of alternating high-Z, low-Z, and composite materials. The composite material layer was deposited by co-sputtering of high-Z and low-Z materials. (2) To achieve smoother zones (multilayer interfaces) at the conventional-type FZP, each target of a sputtering apparatus with two DC-sputtering guns was surrounded by a cover with an aperture, and Ar gas was supplied inside the cover, which led to the deposition at lower Ar gas pressure. As a result, for the former, the efficiency was improved markedly as compared with conventional FZP, and for the latter, the zone roughness was reduced, which has resulted in the improvement of the spatial resolution of the FZP.     

Optimal noise suppression in Fresnel incoherent correlation holography (FINCH) configured for maximum imaging resolution

An optimal setup in the sense of imaging resolution for the Fresnel incoherent correlation holography (FINCH) system is proposed and analyzed. Experimental results of the proposed setup in reflection mode suffer from low signal-to-noise ratio (SNR) due to a granular noise. SNR improvement is achieved by two methods that rely on increasing the initial amount of phase-shifted recorded holograms. In the first method, we average over several independent complex-valued digital holograms obtained by recording different sets of three digital phase-shifted holograms. In the second method, the least-squares solution for solving a system of an overdetermined set of linear equations is approximated by utilizing the Moore-Penrose pseudoinverse. These methods improve the resolution of the reconstructed image due to their ability to reveal fine and weak details of the observed object.     

Imaging with Fresnel zone pupil masks: extended depth of field

Fresnel zone plates are used as pupil apertures to extend the depth of field of an incoherent imaging system. The defocused optical transfer function is evaluated approximately, and the results are confirmed by experiments and by subjective evaluations of the images of a test chart. With a pupil having four zones, for example, the resolution limit at four depths of field out of focus is improved by a factor of 10.     

Observation of kinoform-style multilayer Fresnel zone plate by scanning ion microscopy

We investigated a kinoform-style Fresnel zone plate (FZP) that is a high-efficient optical element for hard X-ray focusing. The Cu/Al kinoform-style FZPs were fabricated with a sputtered-sliced method. The FZP was composed of 450 layers (30 layers, 15 pairs) of Al, Cu/Al composite, and Cu. The microstructure of the Cu/Al composite layer was observed by scanning ion microscopy based on a focused ion beam (FIB). In the Cu/Al composite layer, the SIM images obtained by grain orientation contrast observation indicated that the Cu grains were grown gradually with increasing Cu concentration.     

Channel and substrate zone two-dimensional resolution for chemiluminescent multiplex immunoassay

A two-dimensional resolution system of channels and substrate zones was proposed for multiplex immunoassay performed with a designed multichannel chemiluminescent (CL) detection device coupled with a single photomultiplier. Using carcinoma antigen 125 (CA 125), carcinoma antigen 153 (CA 153), carcinoma antigen 199 (CA 199), and carcinoembryonic antigen (CEA) as two couples of model analytes, two couples of capture antibodies were immobilized in two channels, respectively. With a sandwich format, the CL substrates for alkaline phosphatase and horseradish peroxidase were delivered into the channels sequentially to perform a multiplex immunoassay after the sample and tracer antibodies were introduced into the channels for on-line incubation. CA 125, CA 153, CA 199, and CEA could be assayed in the ranges of 0.50-80, 2.0-100, and 5.0-150 U/mL and 1.0-70 ng/mL with limits of detection of 0.15, 0.80, and 2.0 U/mL and 0.65 ng/mL at 3sigma, respectively. The whole assay process including regeneration of the device could be completed in 37 min. The proposed system showed acceptable detection and fabrication reproducibility, and the results obtained were in acceptable agreement with those from parallel single-analyte test of practical clinical sera. This technique provides a new strategy for a simple, automated, and near-simultaneous multianalyte immunoassay.