Apochromat

About: Apochromat is a research topic. Over the lifetime, 642 publications have been published within this topic receiving 7934 citations.

Hybrid refractive/diffractive achromatic lens for optical data storage systems

Abstract: A diffractive/refractive hybrid lens for use in an optical data storage system as an objective is provided by a convex-plano singlet having a refractive element defined by plano-convex surfaces and a diffractive element defined by a Fresnel zone-like pattern on the plano surface which together provide the total power of the lens. The refractive lens is made of a high index, high dispersion glass so that the curvature and thickness of the refractive lens is minimized while providing a large numerical aperture (at least 0.45) at the expense of increased longitudinal chromatic aberration, which are compensated by the diffractive element and without the need for one or more additional curved surfaces as in low index biaspheric glass objective lenses for chromatic and mono-chromatic aberration reduction, which increases the thickness and curvatures of the lens. The invention enables longitudinal chromatic aberration to be corrected for at least a 10 nm band width around a center wavelength over a 20 nm range, as results when different lasers are used and as laser power varies during optical data storage on an optical data storage device (an optical disk). The thin, light weight low curvature achromat has maximum tolerance for various possible manufacturing errors such as decentering, variations in thickness of the lens, tilt and focal length especially for on-axis field of view less than 2° while providing a very high quality spot (Strehl ratio of at least 0.9.).

Simultaneous Correction of Spherical and Chromatic Aberrations with an Electron Mirror: An Electron Optical Achromat

Abstract: All lenses, whether for light or for electrons, have aberrations that limit their performance. In light optics the invention of the achromat over 200 years ago solved the problem of correcting spherical and chromatic aberrations; however, correcting aberrations of electron lenses remains a challenge. Spherical and chromatic aberrations constitute a fundamental barrier to improving resolution and reducing probe size in various types of electron-optical instruments. Recently, efforts have intensified to reduce probe size in microanalysis and lithography, and to improve resolution in the new emission microscopes being built for synchrotron light sources. The experiments described in this report show how an electron mirror can achieve simultaneous correction of spherical and chromatic aberrations.

Large‐Field‐of‐View Wide‐Spectrum Artificial Reflecting Superposition Compound Eyes

Abstract: In nature, reflecting superposition compound eyes (RSCEs) found in shrimps, lobsters and some other decapods are extraordinary imaging systems with numerous optical features such as minimum chromatic aberration, wide-angle field of view (FOV), high sensitivity to light and superb acuity to motion. Here, we present life-sized, large-FOV, wide-spectrum artificial RSCEs as optical imaging devices inspired by the unique designs of their natural counterparts. Our devices can form real, clear images based on reflection rather than refraction, hence avoiding chromatic aberration due to dispersion by the optical materials. Compared to imaging at visible wavelengths using conventional refractive lenses of comparable size, our artificial RSCEs demonstrate minimum chromatic aberration, exceptional FOV up to 165° without distortion, modest aberrations and comparable imaging quality without any post-image processing. Together with an augmenting cruciform pattern surrounding each focused image, our large-FOV, wide-spectrum artificial RSCEs possess enhanced motion-tracking capability ideal for diverse applications in military, security, medical imaging and astronomy.

Analytic design of hybrid diffractive-refractive achromats.

Abstract: An analytic design of hybrid achromats that combine refractive and diffractive elements is presented. The design procedure does not rely on paraxial approximations and involves two separate stages. In the first stage the chromatic aberrations are corrected for the paraxial rays, and in the second stage the spherical aberrations are corrected by addition of an aspherical phase function to the diffractive element. The residual spherochromatic aberrations of the achromat are evaluated both analytically and numerically, with good agreement between the results. Finally, we illustrate the design procedure by designing a plano-convex achromat for IR radiation with little chromatic dispersion.