Topic
Angular aperture
About: Angular aperture is a research topic. Over the lifetime, 1771 publications have been published within this topic receiving 27257 citations.
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TL;DR: In this paper, the principles underlying acoustic microscopy have been discussed, and examples of acoustic images of fullerite ceramics, metals, and carbon materials are given, together with a review of high-resolution ultrasonic methods.
Abstract: High-resolution ultrasonic methods are briefly reviewed. Special attention is paid to the principles underlying acoustic microscopy, since exactly they provide the high resolution necessary for modern technologies. Examples of acoustic images of fullerite ceramics, metals, and carbon materials are given.
26 citations
Patent•
12 Aug 1994
TL;DR: In this article, a filter consisting of a variable pitch circular grating in front of the focus lens is used to obtain a fraction of the theoretical spot size in a lens system.
Abstract: A fraction of the theoretical spot size in a lens system is obtained by applying a filter consisting of a variable pitch circular grating, in front of the focus lens. The focal point Image of a lens is a spot called an Airy disk. The diameter of the Airy disk is proportional to (wavelength)/(Numerical Aperture). Numerical aperture is equal to (1/2 of the diameter of the lens)/(focal length). This is the theoretical limit of spot size. Using a Bessel Transform, modified circular grating, filter the resulting first and higher order diffraction images lie on the optical axis and interfere resulting in a small beam spot at the focus surrounded by interference bands, producing a narrowed zero order beam for projection in optical and infrared applications.
25 citations
TL;DR: Based on the conjugate-gradient algorithm, a diffractive optical lens with four times depth of focus improvement at the 10.6-µm wavelength has been designed and fabricated as mentioned in this paper.
Abstract: An infrared imaging lens that produces beams with long focal depth while preserving the entire aperture for full light capturing and high transverse resolution is presented. Based on the conjugate-gradient algorithm, a diffractive optical lens with four times depth of focus improvement at the 10.6-µm wavelength has been designed and fabricated. ZEMAX simulation has confirmed the designed lens performance showing legible images over an extended image range. Through laser direct-write photoresist patterning and subsequent reactive ion etching on a germanium substrate, we have realized a diffractive lens with four times depth of focus improvement over a conventional infrared lens of the same numerical aperture. The extended depth of focus lens should yield a variety of applications in focus-free imaging without reducing lens aperture.
25 citations
Patent•
26 Oct 1998
TL;DR: In this paper, the authors proposed a compact, bright wide-angle lens including at least five lens elements, as follows, in order from the object side: a negative lens element, a positive lens element.
Abstract: A compact, bright wide-angle lens including at least five lens elements, as follows, in order from the object side: a negative lens element, a positive lens element, a negative lens element, a positive lens element and a negative lens element. The large aperture, wide-angle lens is provided with favorable image formation capability throughout the entire field of view by arranging, as the negative lens element on the extreme object side, a meniscus lens with its concave surface on the object side, the meniscus lens having at least one aspherical surface and satisfying the following condition: -0.9<(R.sub.1 -R.sub.2)/(R.sub.1 +R.sub.2) where R 1 is the radius of curvature of the surface on the object side of the meniscus lens, and R 2 is the radius of curvature of the surface of the image side of the meniscus lens.
25 citations
TL;DR: In this paper, a wide-beam, full-field, converging lens and pinhole aperture system was used to capture images in a single exposure, and the authors developed an analysis of the system resolution and sensitivity trade-offs.
Abstract: Angular Domain Imaging (ADI) is a high resolution, ballistic imaging method that utilizes the angular spectrum of photons to filter multiply-scattered photons which have a wide distribution of angles from ballistic and quasi-ballistic photons which exit a scattering medium with a small distribution of angles around their original trajectory. Such spatial gating has been previously accomplished using a scanning array of collimating holes micromachined into a silicon wafer section. We now extend that work to include using a wide-beam, full-field, converging lens and pinhole aperture system to capture images in a single exposure. We have developed an analysis of resolution and sensitivity trade-offs of such a system using Fourier optics theory to show that the system resolution is primarily governed by collimation ability at larger aperture sizes and by spatiofrequency (Fourier space-gated) filtering at smaller aperture sizes. It is found that maximum sensitivity is achieved when spatiofrequency resolution and collimation resolution are equal. Planar, high contrast, phantom test objects are observed in 5 cm thick media with effective scattered to ballistic photon ratios >1.25×10 7 :1 using a wide-beam, full-field lens and aperture system. Comparisons are made between ballistic imaging with the lens and aperture system and with the scanning silicon micromachined collimating array. Monte-Carlo simulations with angular tracking validate the experimental results.
25 citations