Israeli researchers find way to create and control elusive terahertz waves

A group of researchers at Tel Aviv University say they have developed a new way to produce and control terahertz waves, an elusive type of electromagnetic wave, using nanometric materials.

These waves can be used to create devices with advanced imaging abilities that can see through opaque materials like plastics or paper, identify small structures and their composition, or look through paint layers in works of art, the researchers said.

Terahertz waves are considered by scientists to be very important due to their unique ability to interact with materials: this makes them useful in accurately identifying different materials. In addition, terahertz waves can pass through materials and objects that appear opaque to other wavelengths, and thus can be used to detect hidden objects and even reveal their composition.

Despite their great importance, however, the ability to produce and control terahertz waves has been very limited compared to other forms of radiation.

Now, researchers at TAU’s Center for Nanoscience and Nanotechnology say they have created nanometric surfaces known as meta-surfaces, which enable the “groundbreaking” and “unprecedented production and control of terahertz waves.”

The nanometric materials were developed at the Nanoscale Electro-Optics Laboratory at TAU’s Department of Physical Electronics, by its head, Prof. Tal Ellenbogen, and research students Shay Keren-Zur, May Tal and Eviatar Minerbi, in collaboration with Prof. Daniel Mittleman of Brown University in the US and Dr. Sharly Fleischer from TAU’s School of Chemistry. The lab for nanoscale electro-optics at the university focuses on the interaction between light and nano-materials.

The results were recently published in both Nature Communications and Nano Letters and will be presented at the beginning of February in the SPIE Photonics West international photonics and laser exhibition in San Francisco.

left to right: Shay Keren-Zur, May Tal, and Prof. Tal Ellenbogen. (Tel Aviv University)

Radio waves and microwaves are long electromagnetic waves; light, X-rays and infrared rays are short electromagnetic waves. Between the short and the long waves on the electromagnetic spectrum reside another kind of electromagnetic waves — the terahertz waves, shorter than radio waves and longer than infrared waves.

The short and long electromagnetic waves already have many uses, thanks to the ability of technology to produce them and control them. But while current technology can create optical waves or radio waves, it cannot create terahertz waves.

The nano-structured materials engineered by the TAU researchers are activated by shining ultra-short pulses of infra-red light at them, and these metamaterials then generate terahertz waves.

By generating application-tailored terahertz waves, the metamaterials provide a promising new tool for terahertz science and applications, the university said in a statement.

The researchers created chips paved with millions of nanometric gold antennas (1 nanometer = 1 billionth of a meter), that get light from lasers emitting ultrashort infrared pulses, and then convert the energy and transmit terahertz pulses instead. By controlling the antennas on the meta-surfaces, the researchers showed that they can control the spatial and temporal shape of the terahertz pulse in a way that had never before been possible.

“The demonstration we performed in the lab breaks new ground, because the use of nanometric materials and the ability to produce light from them in a controllable manner,” said Ellenbogen in a statement. This adds “important technological tools and new abilities, taking research in this field a big step forward.”

“The ability to fully control the spatial shape and other properties of terahertz waves, as demonstrated in the study, enables the development and implementation of advanced imaging methods and new techniques of microscopy and spectroscopy,” he added. “Thus, for example, they will improve the ability to detect from afar, without chemical lab tests, the composition and spatial structure of materials. This will enable, for instance, the easy detection of fake medications and explosives.”

The project received funding from the European Research Council (ERC) and from Israel’s Ministry of Science & Technology.