Thin, flat meta-lenses with tunable features developed

Korean-UK group makes “credit card-thick” metasurface lenses from graphene and gold, to focus terahertz beams.  

http://optics.org/news/8/11/44?webSyncID=776b28d9-cc7c-7cae-388c-544e71035da4&sessionGUID=1ccd516a-90a0-0b40-8604-5dc1a6e754b4&_ga=2.190507624.2107229762.1512083484-178576186.1505831485

                                                                                      

Thinner, flatter: Conventional lens and metalens.

Credit card-thick, flat lenses with tunable features based on graphene and gold have been developed by a partnership of Korean- and UK-based researchers. They say that such optical devices “could become optical components for advanced applications, such as amplitude-tunable lenses, lasers (so-called vortex phase plates), and dynamic holography.”

The scientists work at the Center for Integrated Nanostructure Physics, in the Institute for Basic Science, the Korea Advanced Institute of Science and  Technology and the University of Birmingham. The work has been published in Advanced Optical Materials.

The paper describes the properties of a newly-developed metasurface (a 2D material that can control the electric and magnetic components of light and direct them as wanted) which works as a convex lens. It is made of a gold sheet pierced with micrometer-sized U-shaped holes and covered with graphene.

Conventional solid convex lenses concentrate light on a spot. Similarly with this metasurface, the pattern of apertures of the metalenses focusing the incoming beam. In addition, the microholes can also change light polarization. For example, the metalens can convert the left-circular polarization wave to right-circular polarization (clockwise).

Graphene advantages

The researchers have achieved a conversion rate of 35%. They comment that converting circular polarization could be useful in a number of fields, for example biosensing and telecommunications. To be able to control a range of optical properties, the scientists took advantage of graphene’s unique electronic features and used them to tune the output beam’s intensity or amplitude. The scientists liken graphene’s function to the exposure operation of a camera.                                                                                                                   

        Metalenses’ features.

In the case of the camera, a mechanical control allows a certain shutter’s opening time and size to determine the amount of light entering the instrument. The metalens instead regulates exposure via an electric tension applied to the graphene sheet, without the need for bulky components. When voltage is applied to the graphene layer, the output beam becomes weaker.

'Very sensitive'

“Using metalenses, you can make microscopes, cameras, and tools used in very sensitive optical measurements, much more compact,” clarifies Teun-Teun Kim, lead author of the study.

The metalenses were designed specifically for terahertz radiation. This radiation can pass through some materials such as fabrics and plastics, but at a shorter depth than microwave radiation. For this reason it is employed for surveillance and security screening.

Kim added, “While conventional optical lenses have a thickness of several centimeters to several millimeters, this metalens is just a few tens of micrometers thick. The intensity of the focused light can be effectively controlled and it could find useful applications in ultra-small optical instruments.”

Ultrathin and flat graphene metalenses gain morace properties

Lenses made of graphene and precisely pierced gold sheets are able to concentrate terahertz beams to a spot, flip its polarization and modulate its intensity.

https://www.sciencedaily.com/releases/2017/11/171127124731.htm

On the quest for miniaturization, scientists at the Center for Integrated Nanostructure Physics, within the Institute for Basic Science (IBS, South Korea), in collaboration with researchers from the University of Birmingham and the Korea Advanced Institute of Science and Technology (KAIST), develop credit card-thick, flat lenses with tunable features. These optical devices, made of graphene and a punctured gold surface, could become optical components for advanced applications, such as amplitude tunable lenses, lasers (i.e. vortex phase plates), and dynamic holography.

Metasurfaces are new 2D materials that can effectively control the electric and magnetic components of light (and other electromagnetic waves) and bend them to bespoken directions. Controlling the beam's direction can bring out interesting phenomena; the most incredible being the "invisibility cloak effect," where light waves bypass an object recreating the image beyond the object, as flowing water in a river would bypass a stone.

Published in Advanced Optical Materials, the study presents the properties of a metasurface which works as a convex lens. Specifically, it is made of a gold sheet pierced with micrometer-sized U-shaped holes and covered with graphene. As the shape of common convex lenses allows light to be concentrated on a spot (or focus), think about a magnifying glass which can concentrate a light beam and even start a fire, so the particular pattern of the tiny apertures of the metalenses works by focusing the incoming beam.

In addition, these microholes can also change light polarization. While natural light is generally unpolarized before being reflected, the team used circularly polarized waves, that is a light beam where the direction of the electric field is corkscrew spiraling. This metalens can convert the left-circular polarization wave (going counterclockwise if seen straight in front) to right-circular polarization (clockwise). The researchers managed to obtain a conversion rate of 35%. Converting circular polarization could be useful in a number of fields, for example biosensing and telecommunications.

In order to control even more properties, the scientists took advantage of graphene's unique electronic features and used them to tune the output beam's intensity or amplitude. Here graphene plays the role of the exposure of a camera. In the case of the camera, a mechanical control allows a certain shutter's opening time and size to determine the amount of light entering the instrument. These metalenses instead, regulate the exposure via an electric tension applied to the graphene sheet, without the need for bulky components. When voltage is applied to the graphene layer, the output beam becomes weaker. "Using metalenses, you can make microscopes, cameras, and tools used in very sensitive optical measurements, much more compact," clarifies Teun-Teun Kim, the first author of the study.

The metalenses were designed for a type of electromagnetic wave, which falls in-between infrared radiation and microwave radiation, called terahertz radiation. This type of radiation can pass through some materials (like fabrics and plastics), but at a shorter depth than microwave radiation, for this reason it is employed for surveillance and security screening.

"While conventional optical lenses have a thickness of several centimeters to several millimeters, this metalens is just a few tens of micrometers thick. The intensity of the focused light can be effectively controlled and it could find useful applications in ultra-small optical instruments," highlights the scientists.Teun-Teun Kim, the first author of the study.

KIST team develops AI virus detection sensor

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• By Constance Williams

http://www.koreabiomed.com/news/articleView.html?idxno=1230

A research team, including Dr. Suh Min-ah of Korea Institute of Science and Technology (KIST) Sensor System Research Center, has developed a molecular detection platform to accurately detect various kinds of biomolecules including Avian Influenza viruses.

In recent years, the bird flu caused great damage all around the world including Korea, bringing urgent need for early diagnosis.

The team developed a Terahertz metamaterial for distinguishing and quantifying traces of AI viruses by subtypes, in collaboration with Professor Kang Ji-hoon강지훈 of the University of California at Berkeley, Professor Song Chang-sun송창선 of the College of Veterinary Medicine of Konkuk University건국대 수의과대학, and Professor Park Kyu-hwan박규환 of Korea University고려대 .

Instead of the conventional method to mark the viruses with various indexes, the Terahertz metamaterial can detect viruses label-free using spectroscopic techniques.

KIST research team developed a Terahertz metamaterial, a molecular detection platform using optical and biosensor technology for accurately and quickly detecting viruses.

The traditional process of attaching individual molecules to the chemical/electrical properties may change the nature of the virus, making it difficult to observe the pattern of the virus in the future.

However, the researchers used the inherent optical properties of the immune specific marker for virion, which does not change the nature of the virus. This method is non-contact, especially non-destructive.

"The molecular sensing technology developed in this study can be used to detect trace amounts of molecules selectively. At present, trace quantities of specific DNA and steroids are also validated for detection," said Dr. Suh. "We expect to be applied to diagnostic studies to identify various disease-specific low-molecular substances in the future quickly."

connie@docdocdoc.co.kr

<© KBR , All rights reserved.>

Korea Research Team Discovers Serious Side Effects of Terahertz Radiation

http://www.businesskorea.co.kr/article/5100/side-effects-radiation-korea-research-team-discovers-serious-side-effects-terahertz

A high-precision THz wave irradiation setup for the mouse model.

19 JUNE 2014

Terahertz radiation, formerly thought to be harmless to the human body due to its low energy and to have wider applications than X-rays, has been found to have side effects.  

The Korea Advanced Institute of Science and Technology (KAIST) announced on June 18 that a research team lead by Kim Pil-han, professor of the Graduate School of Nanoscience and Technology at KAIST, and Dr. Jung Young-wook from the Korea Atomic Energy Research Institute discovered symptoms of infections on skin tissue of a test animal exposed to terahertz radiation.

As electromagnetic radiation in the range of 0.1 to 10THz, terahertz radiation is highly penetratable to the extent that it is possible to see the inside of an object like X-rays, owing to their longer wavelength than that of visible and infrared light. Hence, they are used in various areas such as security screening, next-gen wireless mobile communications, and medical imaging technology. Nevertheless, the effects of terahertz radiation on the human body have only rarely been examined.

After developing a high-power terahertz wave generator that can be used on animal bodies, the research team created a high resolution 3D laser scanning microscope. The team exposed a genetically-engineered mouse to high-power terahertz radiation for 30 minutes and observed the skin of the mouse with a 3D laser scanning microscope. They discovered that the number of infected cells increased more than six times after 6 hours of exposure. 

It is the first time to find side effects of terahertz radiation exposure, which were widely acknowledged to have the potential to effectively treat skin diseases such as squamous cell carcinoma without damaging the human body.

The research findings were published online in the May 19 issue of Optics Express, a scientific journal published by the Optical Society of America.

- See more at: http://www.businesskorea.co.kr/article/5100/side-effects-radiation-korea-research-team-discovers-serious-side-effects-terahertz#sthash.77INWTpD.dpuf