Fresnel zone

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

Multilayer on-chip stacked Fresnel zone plates: Hard x-ray fabrication and soft x-ray simulations

Abstract: Fresnel zone plates are widely used as x-ray nanofocusing optics. To achieve high spatial resolution combined with good focusing efficiency, high aspect ratio nanolithography is required, and one way to achieve that is through multiple e-beam lithography writing steps to achieve on-chip stacking. A two-step writing process producing 50 nm finest zone width at a zone thickness of 1.14 μm for possible hard x-ray applications is shown here. The authors also consider in simulations the case of soft x-ray focusing where the zone thickness might exceed the depth of focus. In this case, the authors compare on-chip stacking with, and without, adjustment of zone positions and show that the offset zones lead to improved focusing efficiency. The simulations were carried out using a multislice propagation method employing Hankel transforms.

Positional matching method between mask substrate and wafer

Abstract: PURPOSE:To perform a highly accurate positional matching between the wafer and the mask substrate by a method wherein the image of matching reference to be used for wafers is image formed on the matching reference for masks on the surface of the mask substrate through the intermediary of a Fresnel zone pattern, and the mutual positional information of the mask substrate and the wafer is obtained. CONSTITUTION:The matching reference 2 for wafers is provided on the wafer 1, and at the same time, the matching reference 4 for masks is provided on the surface of the mask substrate 3. Then, the Fresnel zone pattern 5 is formed at the section corresponding to the matching reference 4 for masks located on the reverse side of the mask substrate 3. The image of the matching reference 2 for wafers is image formed on the matching reference 4 for masks located on the surface of the mask substrate 3 through the intermediary of the Fresnel zone pattern 5, matching references 2 and 4 for wafers and masks are superpositioned in the same plane surface, and the mutual positional information on the mask reference 3 and the wafer 1 can be obtained.

Zone-plate diffraction patterns in gradient-index media.

Abstract: Diffraction patterns inside gradient-index media in which a complex zone plate is placed at a Fourier transform plane are studied by making use of the optical propagator. The results are illustrated with an example corresponding to a selfoc medium and a Fresnel zone plate of the amplitude and of the phase.

Lensless joint transform correlator

Abstract: The lensless joint transform correlator optically determines the relative x -y position of two pinholes. The pinholes are placed in parallel arms of a Mach-Zehnder interferometer. The Fraunhaufer diffraction patterns combine to form a joint transform plane. Because of the interference of the two signals, a Fresnel zone is formed in the joint Fraunhaufer diffraction pattern. This is captured and used in a second stage, just as the joint power spectrum is in a joint transform correlator. The joint transform is illuminated with a plane wave, and the output taken in the focal plane of the Fresnel zone. As with the single-lens joint transform correlator, the lensless joint transform correlator exhibits magnification between the input displacement and the output peak displacement. By using the third or fifth order focus of the Fresnel zone, the output resolution can be improved by a factor of three or five in both the x and y dimensions. The output has very good peak-to-noise ratio and position resolution. A peak-to-noise ratio of 106 dB with a resolution of 1.4 µm are observed when using the fifth order focus of the Fresnel zone.