Scientists develop new metasurfaces for deep UV-imaging

December 21, 2016
Schematic sketches of UV generation from (a) smooth and (c) nanostructured Si film. (b) Principle of Si film laser-induced nanostructuring. Credit: ITMO University

Russian researchers have developed a new material that converts infrared light to ultrashort pulses of ultraviolet. For this purpose, the scientists exposed silicon film to a laser so that its relief adjusted under the light wavelength and made properties of the material resonant. The result was a cheap and easy-to-make metasurface as effective as existing ones. The new technology is applicable in compact UV generators for biophotonics and medicine, and also devices for ultradense data processing in optical communications. The study was published in Nanoscale.

Biological media can reflect, absorb, scatter and re-emit light waves. Each of these processes contains information about micro- and macrostructure of the media, as well as shape and motion of its components. In this regard, deep ultraviolet is a promising tool for biology and medicine. Its application includes laser diagnostics and control of fast processes in cells, laser therapy and surgery at the molecular level.

Researchers from ITMO University and Saint Petersburg Academic University have developed a new method for nanostructures fabricating, which is able to convert infrared light to deep ultraviolet. The structure is a film with a regular massive of nanolumps – metasurface. It is generated by radiating silicon film, whose thickness is 100 nanometers, with ultrashort or femtosecond laser pulses that form its relief. On the film surface, the laser smelts such nanolumps, which resonate only with its wavelength and thus allow more radiation to be turned into ultraviolet. In other words, the laser adjusts metasurface to itself. When the relief is formed, the scientists reduce the power so the film starts converting radiation without deformation.

The researchers have managed not only to convert into violet, but also to get deep ultraviolet. Such radiation is strongly localized, has very short wavelength and distributes as femtosecond pulses. "For the first time, we've created a metasurface that stably emits femtosecond pulses of high power in the ultraviolet range," notes Anton Tsypkin, assistant of ITMO's Department of Photonics and Optical Information Technology. "Such light can be applied in biology and medicine, as femtosecond pulses affect biological objects more precisely."

Photography of fluorescence induced by generated UV light in fluorophore. Inset - view of the sample with a self-organized metasurface (orange area). Credit: ITMO University

For example, using deep UV, researchers can image a molecule during its chemical transformation and understand how to manage it. "A femtosecond compared to a second is almost like a second compared to the lifetime of the universe. It's even faster than the vibration of atoms in molecules. So such short pulses can tell us a lot about matter structure in motion," says first author Sergey Makarov, senior research associate of ITMO's Department of Nano-Photonics and Metamaterials.

The may also find applications in . "Using for data transmission, we will make the flow denser and enhance its speed. It will increase the performance of systems for transferring and processing information. Additionally, we can integrate such metasurfaces into an optical chip to change beam frequency. This will help separate data flows and enable major computing at the same time," comments Anton Tsypkin.

The metasurface obtained in this way is a monolithic structure, as opposed to being assembled of isolated particles, as it was before. It conducts heat better and thus lives longer without overheating.

In photonics, researchers always have to search for compromise. Standard nonlinear crystals used for ultraviolet generation are big, but can convert up to 20 percent of radiation. Such efficiency is higher than that of metasurfaces, but laser pulses lengthen inside crystals. "This happens because a laser beam contains many wavelengths that differ from each other only by several decades of nanometers. Such variance is enough to make some waves surpass others. In order to make pulses ultrashort again, additional expensive devices are required," explains Makarov.

Thin structures such as metasurfaces do not allow to misalign, but still have a low efficiency. Furthermore, both metasurfaces and crystals are usually expensive and difficult to make. However, in the new study, the scientists have managed to make metasurface fabrication much easier and cheaper, and at the same time, these surfaces are as effective as their expensive counterparts.

Explore further: Versatile optical laser will enable innovative experiments at atomic-scale measurements

More information: S. V. Makarov et al. Self-adjusted all-dielectric metasurfaces for deep ultraviolet femtosecond pulse generation, Nanoscale (2016). DOI: 10.1039/C6NR04860A

Related Stories

Scientists count microscopic particles without a microscope

August 10, 2016

Scientists from Russia and Australia have proposed a simple new way of counting microscopic particles in optical materials by means of a laser. A light beam passing through such a material splits and forms a characteristic ...

A sense for infrared light

January 19, 2016

Laser physicists from the Max Planck Institute of Quantum Optics developed a measuring system for light waves in the near-infrared range.

Recommended for you

Graphene photodetector enhanced by fractal golden 'snowflake'

January 16, 2017

(Phys.org)—Researchers have found that a snowflake-like fractal design, in which the same pattern repeats at smaller and smaller scales, can increase graphene's inherently low optical absorption. The results lead to graphene ...

Nanoscale view of energy storage

January 16, 2017

In a lab 18 feet below the Engineering Quad of Stanford University, researchers in the Dionne lab camped out with one of the most advanced microscopes in the world to capture an unimaginably small reaction.

Scientists create first 2-D electride

January 11, 2017

(Phys.org)—Researchers have brought electrides into the nanoregime by synthesizing the first 2D electride material. Electrides are ionic compounds, which are made of negative and positive ions. But in electrides, the negative ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.