Fresnel zone

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

Precision Alignment Using a System of Large Rectangular Fresnel Lenses

Abstract: A system of large rectangular Fresnel lenses has been used in the laser alignment system for the SLAC two-mile accelerator. The alignment system consists of a He–Ne laser light source, a photoelectric detector, and the lenses, one of which is located at each of 297 points which are to be aligned. Each lens has the proper focal length to focus the laser to a point image at the detector. When the alignment at a certain point is to be checked, the image from that lens is scanned by the detector. The image is found to be displaced from its normal position by an amount equal to the product of the position error and the magnification of the lens. The alignment sensitivity is ±0.0025 mm. The targets are enclosed in a 60-cm diam evacuated light pipe to avoid atmospheric disturbances.

Fabrication of Fresnel plates on optical fibres by FIB milling for optical trapping, manipulation and detection of single cells.

Abstract: The development of economical optical devices with a reduced footprint foreseeing manipulation, sorting and detection of single cells and other micro particles have been encouraged by cellular biology requirements. Nonetheless, researchers are still ambitious for advances in this field. This paper presents Fresnel zone and phase plates fabricated on mode expanded optical fibres for optical trapping. The diffractive structures were fabricated using focused ion beam milling. The zone plates presented in this work have focal distance of ~5 µm, while the focal distance of the phase plates is ~10 µm. The phase plates are implemented in an optical trapping configuration, and 2D manipulation and detection of 8 µm PMMA beads and yeast cells is reported. This enables new applications for optical trapping setups based on diffractive optical elements on optical fibre tips, where feedback systems can be integrated to automatically detect, manipulate and sort cells.

Optical Manipulation along an Optical Axis with a Polarization Sensitive Meta-Lens.

Abstract: The ability to manipulate small objects with focused laser beams opens a broad spectrum of opportunities in fundamental and applied studies, for which precise control over mechanical path and stability is required. Although conventional optical tweezers are based on refractive optics, the development of compact trapping devices that could be integrated within fluid cells is in high demand. Here, a plasmonic polarization-sensitive metasurface-based lens, embedded within a fluid, is demonstrated to provide several stable trapping centers along the optical axis. The position of a particle is controlled with the polarization of the incident light, interacting with plasmonic nanoscale patch antennas, organized within overlapping Fresnel zones of the lens. While standard diffractive optical elements face challenges in trapping objects in the axial direction outside the depth of focus, bifocal Fresnel meta-lens demonstrates the capability to manipulate a bead along a 4 μm line. An additional fluorescent module, ...

Maximum power transfer between two planar apertures in the Fresnel zone

Abstract: This paper is concerned with the problem of finding the illuminations on two planar antennas (directed toward each other) which maximize the efficiency of the power transfer between them. The two apertures are generally different and their separation, sizes, and shapes are arbitrary (with the exception of some symmetry requirements). It is shown that the optimal phase distributions are such that the two antennas are focused on each other. The optimal amplitude distributions are equal to the field patterns of the mode with minimum diffraction loss in two confocal resonator mirrors, whose separation, sizes, and shapes are equal to those of the apertures in question. For the particular case of rectangular antennas, the optimal amplitude distributions are given by Prolate Spheroidal Wave Functions. The Power Transfer Coefficient between two equal square apertures has been calculated for optimal and uniform (focused and unfocused) illuminations. For moderate to small separations the optimal illuminations yield a very significant increase of the efficiency of the power transfer.

High-efficiency nickel phase zone plates with 20 nm minimum outermost zone width

Abstract: Fresnel zone plates for high-resolution imaging in the soft x-ray regime were fabricated in nickel by a trilevel process, which makes use of electron-beam lithography, reactive-ion etching, and electrodeposition. In order to improve the zone plate’s resolution, which is determined by its outermost zone width, ZEP-7000 electron-beam resist was employed. Residues, which arose during pattern transfer by reactive-ion etching, and which hindered etching in small structures, were suppressed by a cleaning procedure. For improved electrodeposition process control, a nickel electroplating bath was optimized. Zone plates with minimum outermost zone widths of 20, 25 and 30 nm were fabricated, yielding 9.2%, 16.2% and 18.0% first-order diffraction efficiency, respectively, at λ=2.4 nm.