Focusing properties of Fresnel zone plates with spiral phase
TL;DR: 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.
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.
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TL;DR: The general propagation dynamics of an Airy beam (AiB) carrying unit phase singularity, i.e., optical vortices (OVs) are demonstrated.
Abstract: In this Letter, we demonstrate the general propagation dynamics of an Airy beam (AiB) carrying unit phase singularity, i.e., optical vortices (OVs). For the OV with a unit charge, theoretical analysis indicates that the OV carried by the AiB will propagate along the parabolic trajectory with an acceleration velocity twice as fast as conventional AiBs before a critical position. Thereafter, the AiB main lobe destroyed by OV will be reconstructed and the phase singularity will reappear in the middle of the AiB profile.
102 citations
42 citations
TL;DR: In this article, the authors address the needs of scientists and engineers who desire to generate/detect OAM modes and are looking for the technique (active or passive) best suited for their application.
Abstract: Orbital angular momentum (OAM), one of the most recently discovered degrees of freedom of light beam field has fundamentally revolutionized optical physics and its technological capabilities. Optical beams with OAM have enabled a large variety of applications, including super-resolution imaging, optical trapping, classical and quantum optical communication, and quantum computing, to mention a few. To enable these and several other emerging applications, optical beams with OAM have been generated using a variety of methods and technologies, such as a simple astigmatic lens pair, one-/two-dimensional holographic optical elements, three-dimensional spiral phase plates, optical fibers, and recent entrants such as metasurfaces. All these techniques achieve spatial light modulation and can be implemented with either passive elements or active devices, such as liquid crystal on silicon and digital micromirror devices. Many of these devices and technologies are not only used for the generation of amplitude phase-polarization structured light beams but are also capable of analyzing them. We have attempted to encompass a wide variety of such technologies as well as a few emerging methodologies, broadly categorized into generation and detection protocols. We address the needs of scientists and engineers who desire to generate/detect OAM modes and are looking for the technique (active or passive) best suited for their application.
40 citations
TL;DR: The CSFZP beam pattern was implemented in an optical trapping experiment and was found to possess particle trapping capabilities, with a strong central focal spot and twisted side lobes.
Abstract: In this study, we introduce what we believe is a novel holographic optical element called a chiral square Fresnel zone plate (CSFZP) The chirality is imposed on a square Fresnel zone plate (SFZP) using a nonclassical technique by rotating the half-period zones relative to one another The rotation of the half-period zones, in turn, twists the side lobes of the diffraction pattern without altering the focusing properties inherent to a SFZP As a consequence, the beam profile is hybrid, consisting of a strong central Gaussian focal spot with gradient force similar to that generated by a lens and twisted side lobes with orbital angular momentum The optical fields at the focal plane were calculated and found to possess a whirlpool-phase profile and a twisted intensity profile Analysis of the field variation along the direction of propagation revealed a spiraling phase and amplitude distribution Poynting vector plot of the fields revealed the presence of angular momentum in the regions of chiral side lobes The phase of the CSFZPs were displayed on a phase-only reflective spatial light modulator and illuminated using a laser The intensity patterns recorded in the experiment match the calculated ones, with a strong central focal spot and twisted side lobes The beam pattern was implemented in an optical trapping experiment and was found to possess particle trapping capabilities
24 citations
TL;DR: In this article, a diffractive element is proposed to produce a perfect vortex beam by shifting the phase of a spiral zone plate and demonstrate how the phase shift enables managing the size of the generated perfect vortex.
Abstract: We propose a novel diffractive element to produce a perfect vortex beam. Flexibility in creating any perfect vortex beam is one of the considerable advantages of this method. Moreover, simplicity in creating the element is another interesting feature of this technique. We simply produce the proposed element by shifting the phase of a spiral zone plate and demonstrate how the phase shift enables us to manage the size of the generated perfect vortex. Further studies illustrate that the shape of the vortex is preserved in a long focal depth, while the phase map rotates around the propagation axis. In addition, all experimental results denote congruence with the respective results from simulation.
21 citations
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TL;DR: The achievement of sub-15-nm spatial resolution with a soft X-ray microscope—and a clear path to below 10 nm—using an overlay technique for zone plate fabrication is reported.
Abstract: The study of nanostructures is creating a need for microscopes that can see beyond the limits of conventional visible light and ultraviolet microscopes. X-ray imaging is a promising option. A new microscope described this week achieves unprecedented resolution, and has the ability to see through containing material. It features a specially made two-component zone plate — a lens with concentric zones rather like the rings in the Fresnel lenses familiar in overhead projectors and elsewhere — that makes use of diffraction to project an image into a CCD camera sensitive to soft X-rays. Spatial resolution of better than 15 nm is possible. Analytical tools that have spatial resolution at the nanometre scale are indispensable for the life and physical sciences. It is desirable that these tools also permit elemental and chemical identification on a scale of 10 nm or less, with large penetration depths. A variety of techniques1,2,3,4,5,6,7 in X-ray imaging are currently being developed that may provide these combined capabilities. Here we report the achievement of sub-15-nm spatial resolution with a soft X-ray microscope—and a clear path to below 10 nm—using an overlay technique for zone plate fabrication. The microscope covers a spectral range from a photon energy of 250 eV (∼5 nm wavelength) to 1.8 keV (∼0.7 nm), so that primary K and L atomic resonances of elements such as C, N, O, Al, Ti, Fe, Co and Ni can be probed. This X-ray microscopy technique is therefore suitable for a wide range of studies: biological imaging in the water window8,9; studies of wet environmental samples10,11; studies of magnetic nanostructures with both elemental and spin-orbit sensitivity12,13,14; studies that require viewing through thin windows, coatings or substrates (such as buried electronic devices in a silicon chip15); and three-dimensional imaging of cryogenically fixed biological cells9,16.
842 citations
TL;DR: It is shown that a large number of pinholes distributed appropriately over the Fresnel zones make it possible to focus soft X-rays to spot sizes smaller than the diameter of the smallest pinhole.
Abstract: Fresnel zone plates consisting of alternating transmissive and opaque circular rings can be used to focus X-rays1. The spatial resolution that can be achieved with these devices is of the order of the width of the outermost zone and is therefore limited by the smallest structure (20–40 nm) that can be fabricated by lithography today2. Here we show that a large number of pinholes distributed appropriately over the Fresnel zones make it possible to focus soft X-rays to spot sizes smaller than the diameter of the smallest pinhole. In addition, higher orders of diffraction and secondary maxima can be suppressed by several orders of magnitude. In combination with the next generation of synchrotron light sources (free-electron lasers) these ‘photon sieves’ offer new opportunities for high-resolution X-ray microscopy and spectroscopy in physical and life sciences.
362 citations
TL;DR: In this article, the authors report the fabrication of high-efficiency, high-contrast gold and nickel multistep (quaternary) Fresnel zone plates using electron beam lithography.
Abstract: The development of high brilliance X-ray sources coupled with advances in manufacturing technologies has led to significant improvements in submicrometre probes for spectroscopy, diffraction and imaging applications. The generation of a small beam spot size is commonly based on three principles1: total reflection (as used in optical elements involving mirrors or capillaries), refraction (such as in refractive lenses2) and diffraction. The latter effect is employed in Bragg–Fresnel or Soret lenses, commonly known as Fresnel zone plate lenses. These lenses currently give the best spatial resolution, but are traditionally limited to rather soft X-rays—at high energies, their use is still limited by their efficiency. Here we report the fabrication of high-efficiency, high-contrast gold and nickel multistep (quaternary) Fresnel zone plates using electron beam lithography. We achieve a maximum efficiency of 55% for the nickel plate at 7 keV. In addition to their high efficiency, the lenses offer the advantages of low background signal and effective reduction of unwanted diffraction orders. We anticipate that these lenses should have a significant impact on techniques such as microscopy3, micro-fluorescence4 and micro-diffraction5, which require medium resolution (500–100 nm) and high flux at fixed energies.
274 citations
TL;DR: Testing of the zone plate with the full-field transmission x-ray microscope, XM-1, in Berkeley, showed that the lens clearly resolved 12 nm lines and spaces, a significant step towards 10 nm resolution and beyond.
Abstract: To extend soft x-ray microscopy to a resolution of order 10 nm or better, we developed a new nanofabrication process for Fresnel zone plate lenses. The new process, based on the double patterning technique, has enabled us to fabricate high quality gold zone plates with 12 nm outer zones. Testing of the zone plate with the full-field transmission x-ray microscope, XM-1, in Berkeley, showed that the lens clearly resolved 12 nm lines and spaces. This result represents a significant step towards 10 nm resolution and beyond.
273 citations
TL;DR: A radially symmetric Hilbert transform is introduced that permits two-dimensional edge enhancement and is implemented with a programmable phase-only liquid-crystal spatial light modulator.
Abstract: The Hilbert transform is useful for image processing because it can select which edges of an input image are enhanced and to what degree the edge enhancement occurs. However, the transform operation is one dimensional and is not applicable for arbitrarily shaped two-dimensional objects. We introduce a radially symmetric Hilbert transform that permits two-dimensional edge enhancement. We implement one-dimensional, two-dimensional, and radial Hilbert transforms with a programmable phase-only liquid-crystal spatial light modulator. Experimental results are presented.
249 citations