Fresnel zone

About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.

Wave propagation in optical systems with large apertures

Abstract: The Kirchhoff-Huygens equation is used to investigate wave propagation in optical systems, with large propagation Fresnel numbers NF and aperture-to-length ratios (a/L) which are not small. The limit of applicability of the Fresnel approximation is analytically established for a thin rectangular aperture. It is shown that the error introduced by the Fresnel approximation to the Kirchhoff integral is comparable to the effects of diffraction, computed by the approximation, times the dimensionless parameter πNF(a/2L)2.

A Low-Cost NLOS Identification and Mitigation Method for UWB Ranging in Static and Dynamic Environments

Abstract: This letter proposes a low-cost non-line-of-sight (NLOS) identification and mitigation technique for ultra-wideband (UWB) ranging in both static and dynamic environments. Unlike conventional ranging that employs one mobile tag and a single fixed anchor at a known location, this technique utilizes two anchors and one tag. By utilizing Fresnel zones, this approach is effective in variable environments without requiring large quantities of prior knowledge. The proposed method was evaluated using simulations and experiments, achieving an identification accuracy of 96.41%. After error mitigation, ranging errors were reduced by 88.80%, 69.91%, and 96.12% in line-of-sight (LOS), NLOS, and dynamic NLOS environments, respectively.

Optimization-free approach for generating sub-diffraction quasi-non-diffracting beams.

Abstract: Sub-diffraction quasi-non-diffracting beams with sub-wavelength transverse size are attractive for applications such as optical nano-manipulation, optical nano-fabrication, optical high-density storage, and optical super-resolution microscopy. In this paper, we proposed an optimization-free design approach and demonstrated the possibility of generating sub-diffraction quasi-non-diffracting beams with sub-wavelength size for different polarizations by a binary-phase Fresnel planar lens. More importantly, the optimization-free method significantly simplifies the design procedure and the generation of sub-diffracting quasi-non-diffracting beams. Utilizing the concept of normalized angular spectrum compression, for wavelength λ0 = 632.8 nm, a binary-phase Fresnel planar lens was designed and fabricated. The experimental results show that the sub-diffraction transverse size and the non-diffracting propagation distances are 0.40λ0–0.54λ0 and 90λ0, 0.43λ0–0.54λ0 and 73λ0, and 0.34λ0–0.41λ0 and 80λ0 for the generated quasi-non-diffracting beams with circular, longitudinal, and azimuthal polarizations, respectively.

Spatial Coherence in Periodic Systems

Abstract: The van Cittert–Zernike theorem states that quasimonochromatic light from a spatially incoherent source, propagating in free space, will increase in spatial coherence Wolf has shown that quasimonochromatic light, which is initially only partially space coherent or even incoherent, may become coherent upon propagating through a periodic system of apertures In this paper we employ the mode theory of optical resonators and transmission systems to obtain the results of the van Cittert–Zernike theorem and to study the rapidity with which coherence builds up in periodic systems of apertures and confocal lenses A perturbation calculation for modes in circular geometries with small Fresnel numbers is included

Real space soft x-ray imaging at 10 nm spatial resolution

Abstract: Real Space Soft X-ray Imaging at 10 nm Spatial Resolution W. Chao 1 , P. Fischer 1 , T. Tyliszczak 2 , S. Rekawa 1 , E. Anderson 1 , and P. Naulleau 1 Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 Using Fresnel zone plates made with our robust nanofabrication processes, we have successfully achieved 10 nm spatial resolution with soft x-ray microscopy. The result, obtained with both a conventional full-field and scanning soft x-ray microscope, marks a significant step forward in extending the microscopy to truly nanoscale studies. PACS: 68.37.Yz, 42.79.Ci The scientific interest and technological importance of nanoscale phenomena have triggered the development of a plethora of characterization techniques, including imaging tools with high spatial resolution. Soft x-ray microscopy is of particular interest, since it offers a unique combination of properties, such as the short wavelength of soft x-rays, which allows for nanometer spatial resolution, the elemental specific photoabsorption, and the ultrashort soft x-ray pulses at the upcoming soft x-ray sources such as free electron lasers (FEL). It opens new research avenues in a myriad of fields including material sciences, biology, environmental science, and astrophysics [1]. For example, a spatial resolution to below 10 nm could facilitate investigation of the internal structures of nanoparticles and magnetic vortex cores [2-4], engineering of organic photovoltaic materials [5], and understanding of catalyst chemistry in energy science [6]. Here, we report the achievement of 10nm spatial resolution with soft x-ray microscopy, using both the conventional full-field and scanning imaging technique. To our knowledge, the result is one of the best achieved to date. Although a similar result was demonstrated recently using a novel zone plate design at a scanning transmission soft x-ray microscope (STXM) [7], the result here was obtained with a simpler zone plate fabrication process. The designs of conventional transmission soft x-ray microscopes (TXM) and STXMs have been described elsewhere [8, 9]. In brief, a conventional TXM condenses x-rays by a large zone plate onto the sample, which in turn is imaged by a “micro” zone plate downstream (Fig 1). An incoherent bend magnet source is used. In an STXM, a zone plate focuses x-rays to a small spot on the sample. The sample is raster scanned by the spot, and the transmitted x-rays are collected by a detector downstream. To obtain a small scanning spot for high spatial resolution, the focusing zone plate is