Lens (optics)

About: Lens (optics) is a research topic. Over the lifetime, 156482 publications have been published within this topic receiving 1244415 citations.

A compound refractive lens for focusing high-energy X-rays

Abstract: THE development of techniques for focusing X-rays has occupied physicists for more than a century. Refractive lenses, which are used extensively in visible-light optics, are generally considered inappropriate for focusing X-rays, because refraction effects are extremely small and absorption is strong. This has lead to the development of alternative approaches1,2 based on bent crystals and X-ray mirrors, Fresnel and Bragg–Fresnel zone plates, and capillary optics (Kumakhov lenses). Here we describe a simple procedure for fabricating refractive lenses that are effective for focusing of X-rays in the energy range 5–40 keV. The problems associated with absorption are minimized by fabricating the lenses from low-atomic-weight materials. Refraction of X-rays by one such lens is still extremely small, but a compound lens (consisting of tens or hundreds of individual lenses arranged in a linear array) can readily focus X-rays in one or two dimensions. We have fabricated a compound lens by drilling 30 closely spaced holes (each having a radius of 0.3 mm) in an aluminium block, and we demonstrate its effectiveness by focusing a 14-keV X-ray beam to a spot size of 8 μm.

The focusing of electron flow and a Veselago lens in graphene p-n junctions.

Abstract: The focusing of electric current by a single p-n junction in graphene is theoretically predicted. Precise focusing may be achieved by fine-tuning the densities of carriers on the n- and p-sides of the junction to equal values. This finding may be useful for the engineering of electronic lenses and focused beam splitters using gate-controlled n-p-n junctions in graphene-based transistors.

The Axicon: A New Type of Optical Element

Abstract: A search for a universal-focus lens has led to a new class of optical elements. These are called axicons. There are many different kinds of axicons but probably the most important one is a glass cone. It may be either transmitting or reflecting. Axicons form a continuous straight line of images from small sources.One application is in a telescope. The usual spherical objective is replaced by a cone. This axicon telescope is in focus for targets from a foot or so to infinity without the necessity of moving any parts. It can be used to view simultaneously two or more small sources placed along the line of sight.If a source of light is suitably added to the telescope it becomes an autocollimator. Like ordinary autocollimators it can be used to determine the perpendicularity of a mirror. In addition, it can simultaneously act as a telescope for a point target which may be an illuminated pinhole in the mirror.The axicon autocollimator is also a projector which projects a straight line of images into space.

Electron microscopy image enhanced

Abstract: One of the biggest obstacles in improving the resolution of the electron microscope has always been the blurring of the image caused by lens aberrations. Here we report a solution to this problem for a medium-voltage electron microscope which gives a stunning enhancement of image quality.

Adaptive liquid microlenses activated by stimuli-responsive hydrogels

Abstract: The trend towards miniaturization in optical imaging, diagnostics and lab-on-a-chip technology is creating a demand for sophisticated microlenses. A new type of smart liquid microlens has been developed that differs from most current devices in that it is self-focusing. The key component is a stimuli-responsive hydrogel integrated into a microfluidic system and acting as a container for a liquid droplet. The hydrogel simultaneously senses stimuli and actuates a change in droplet shape — and hence focal length. Stimuli can include biological and chemical agents and physical parameters. At this micrometre scale, pinned liquid-liquid interfaces are used to attain stable devices, and response times of ten to a few tens of seconds. Lenses can have virtually any focal length and are readily integrated into arrays. Despite its compactness, the human eye can easily focus on different distances by adjusting the shape of its lens with the help of ciliary muscles1. In contrast, traditional man-made optical systems achieve focusing by physical displacement of the lenses used. But in recent years, advances in miniaturization technology have led to optical systems that no longer require complicated mechanical systems to tune and adjust optical performance. These systems have found wide use in photonics, displays and biomedical systems. They are either based on arrays of microlenses with fixed focal lengths2,3,4,5, or use external control to adjust the microlens focal length6,7,8,9,10,11,12. An intriguing example is the tunable liquid lens, where electrowetting or external pressure manipulates the shape of a liquid droplet and thereby adjusts its optical properties. Here we demonstrate a liquid lens system that allows for autonomous focusing. The central component is a stimuli-responsive hydrogel13 integrated into a microfluidic system and serving as the container for a liquid droplet, with the hydrogel simultaneously sensing the presence of stimuli and actuating adjustments to the shape—and hence focal length—of the droplet. By working at the micrometre scale where ionic diffusion and surface tension scale favourably14, we can use pinned liquid–liquid interfaces to obtain stable devices and realize response times of ten to a few tens of seconds. The microlenses, which can have a focal length ranging from -∞ to +∞ (divergent and convergent), are also readily integrated into arrays that may find use in applications such as sensing, medical diagnostics and lab-on-a-chip technologies15,16,17,18,19.