Fresnel zone

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

Holographic radius test plates for spherical surfaces with large radius of curvature

Abstract: We describe a novel interferometric method, based on nested Fresnel zone lenses or photon sieves, for testing and measuring the radius of curvature of precision spherical surfaces that have radii in a range between several meters and a few hundred meters. We illustrate the measurement concept with radius measurements of a spherical mirror with a radius of about 10 m. The measured radius is 9877 mm±10 mm for a coverage factor k=2. Our measurements also demonstrate, for the first time to the best of our knowledge, the utility of photon sieves for precision surface metrology because they diffuse higher diffraction orders of computer generated holograms, which reduces coherent noise.

Reconfigurable diffractive antenna with three degrees of freedom

Abstract: Diffractive antennas implement steerable beams based on reconfigurable diffractive devices such as Fresnel zone plates (FZPs). Compared with phased array systems, FZP antennas have concise architectures and simple beam-steering mechanisms. In this Letter, the authors demonstrate an FZP-based reconfigurable diffractive antenna with three degrees of freedom (3DoF), i.e. simultaneous reconfigurable steering angle, beamwidth and operating frequency. Such a highly reconfigurable antenna is implemented based on a single-layer metasurface mounted with microwave varactors. The principle behind this 3DoF reconfiguration is the electrically induced transparency and opacity switched by different sets of binary voltages applied across the varactors. Experimental measurements validated the proposed approach.

Microfabrication of Fresnel zone plates by laser induced solid ablation

Abstract: A novel and simple single-step method of inscribing optical elements on metal-coated transparent substrates is demonstrated. Laser induced solid ablation (LISA) demands very low laser energies (nJ), as can be amply provided by a femtosecond laser oscillator. Here, LISA is used to write Fresnel zone plates on indium and tungsten coated glass. With up to 100 zones, remarkable agreement is obtained between measured and expected values of the focal length. LISA has enabled attainment of focal spot sizes that are 38% smaller than what would be obtained using conventional lenses of the same numerical aperture. The simplicity with which a high degree of automation can readily be achieved using LISA makes this cost-effective method amenable to a wide variety of applications related to microfabrication of optical elements.

Comparative simulations of Fresnel holography methods for atomic waveguides

Abstract: We have simulated the optical properties of micro-fabricated Fresnel zone plates (FZPs) as an alternative to spatial light modulators (SLMs) for producing non-trivial light potentials to trap atoms within a lensless Fresnel arrangement. We show that binary (1-bit) FZPs with wavelength (1 \mu m) spatial resolution consistently outperform kinoforms of spatial and phase resolution comparable to commercial SLMs in root mean square error comparisons, with FZP kinoforms demonstrating increasing improvement for complex target intensity distributions. Moreover, as sub-wavelength resolution microfabrication is possible, FZPs provide an exciting possibility for the creation of static cold-atom trapping potentials useful to atomtronics, interferometry, and the study of fundamental physics.

Lensless imaging from diffraction intensity measurements by use of a noniterative phase-retrieval method.

Abstract: A method of reconstructing the complex amplitude of an object that is illuminated by a coherent wave from its Fresnel diffraction patterns is proposed for high-frequency wave phenomena such as x-rays and electron waves. A noniterative phase-retrieval method that uses a Gaussian filter is employed here, and it is shown that the object's illumination with amplitude distribution in the Fraunhofer diffraction pattern of a circular aperture can be used as a substitute for the Gaussian filter. This method has an advantage over other noniterative phase-retrieval methods in that it can retrieve phase vortices.