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article imageEssential Science: Flat lens leads advances in optics

By Tim Sandle     Jun 6, 2016 in Science
A groundbreaking invention from U.S. scientists has shown how optics can be taken to a new level. The lens is an example of advancements in metamaterials, an emerging field in physics.
The advancement sounds simple: it consist of a flat lens made of paint whitener on a sliver of glass. The lens is, however, an example of the latest advances in metamaterials. The lens is lightweight, only 2 millimetres in diameter and the thickness of a human hair.
The lens can produce clear magnification of nanoscale objects, which helps with the latest developments in the fast-paced field of nanotechnology; it also allows for clearer images as viewed through microscopes.
An undated photo from the British Health Protection Agency shows the Coronavirus seen under an elect...
An undated photo from the British Health Protection Agency shows the Coronavirus seen under an electron miscroscope
, British Health Protection Agency/AFP
Metamaterials is a relatively new scientific field, which examines the properties of materials based on variations to the material structure. Although variations in shape have been taking place for a few years; variations in shape to alter mechanical properties is something new. The creation of a metamaterial means the development of a material that has been engineered to have a property that is not found in nature. Such materials are normally fashioned from metals or plastics.
The process of creating metamaterials is very exact. It is the precise shape, geometry, size, orientation and arrangement that delivers the special properties. These alterations give the materials so-called "smart properties," including the ability to alter anything from within the electromagnetic spectrum, including light. Here waves can be blocked, absorbed, enhanced, or bent.
Light dispersion of a mercury-vapor lamp with a prism made of flint glass.
Light dispersion of a mercury-vapor lamp with a prism made of flint glass.
D-Kuru (CC BY-SA 3.0 AT)
Applications of the metamaterial technology include medical devices, sensor detection solar power management, high-frequency battlefield communication high-gain antennas. For example, researchers at the California Institute of Technology have produced very small ceramics that do something entirely unprecedented: they spring back after being squashed by up to 50 percent.
Scientists discovered the shapes on the surfaces of the lenses lead to different optical properties. Standard lenses are curved discs of glass. The new lenses are rendered from transparent quartz and covered in millions of tiny structures that resemble pillars. The pillars are incredibly tiny, with dimensions of just tens of nanometres across and hundreds of nanometers high.
With the new lenses, these were configured so that the surface structure of this lens was smaller than the wavelength of light involved: a thousandth of a millimetre. Having scales that are smaller than the wavelengths of the phenomena they influence, is the key property. This effect is due to the millions of pillars affixed to the lens surface. It is with the pillars that paint whitener comes in. Paint-whitener (titanium dioxide) is used to make the pillars.
Each individual pillar interacts with light. The combination effect of the pillars serves to slice up a light beam and then remould it as the rays pass through the pillar array. Changing the change the size, spacing and orientation of the pillars leads to different focal lengths.
The concept is outlined in the following video:
The structure of the lens, and the precise arrangement of the pillars, required the use of a sophisticated computer program. The lenses are more accurate because they do not have the aberrations found with traditional glass optics.
Speaking with BBC Science, the lead researcher, Dr. said Federico Capasso, who is based at Harvard University, said: "In my opinion, this technology will be game-changing."
In terms of applications, the lenses will be used in nanoscience. They could also prove useful with smartphones, and help push the camera in the phone to a new level of definition.
The lens and associated technology is described in the journal Science. The research paper is titled "Metalenses at visible wavelengths: Diffraction-limited focusing and subwavelength resolution imaging."
The new technology has created interest on Twitter, with New Scientist providing more background information, together with images of the technology. FUTURISTECH INFO stated that the technology will produce more sophisticated microscopes; and Hacker News enthused the process will lead to a "possible revolution in optics."
This article is part of Digital Journal's regular Essential Science columns. Each week we explore a topical and important scientific issue. Last week the topic of sending ultrasonic signals through animals tissue in order to program medical devices was presented. The week before we looked at the design of flying robots, based on static electricity to adhere to the underside of a leaf and to rest on other materials.
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