Researchers discover anti-laser masquerading as perfect absorber

February 15, 2019 by Ken Kingery, Duke University
The width, height and spacing of the cylinders depicted here dictates how the metamaterial described in the new paper absorbs electromagnetic energy. Credit: Kebin Fan, Duke University

Researchers at Duke University have discovered that a perfect absorber of electromagnetic waves they described in a 2017 paper can easily be tweaked into a sort of "time-reversed laser" known as a coherent perfect absorber (CPA).

The research appeared online on January 28 in the journal Advanced Optical Materials.

A laser is a device that transforms energy into coherent light, meaning the are perfectly aligned with one another. Reversing the process, a CPA—sometimes called a time-reversed laser—is a device that absorbs all of the energy from two identical electromagnetic waves hitting it from either side in perfect synchrony. That is, the crests and troughs of their waves enter the material from either side at precisely the same time.

In 2017, Willie Padilla, professor of electrical and computer engineering at Duke, built the first material capable of absorbing nearly 100 percent of an electromagnetic wave's energy without containing even an atom of metal. The device was a metamaterial— composed of many individual, engineered features that together produce properties not found in nature.

This particular metamaterial featured zirconia ceramic constructed into a surface dimpled with cylinders like the face of a Lego brick. After computationally modeling the device's properties by altering the cylinders' size and spacing, the researchers realized that they had actually created a more fundamental kind of CPA.

Picture of the actual metamaterial consisting of a field of specifically tailored cylinders. Credit: Willie Padilla, Duke University
"We've studied this system before as a perfect absorber, but now we've figured out that this device can be configured to be a CPA as well," said Padilla. "This study has shown that these seemingly different fields are actually one and the same."

The CPAs currently described in the literature all have only one mode. They work when the incoming electromagnetic waves are either perfectly aligned or perfectly out of sync. Padilla and Kebin Fan, a research assistant professor in Padilla's laboratory, have discovered that their perfect absorber is actually a CPA with two overlapping modes: it can absorb both aligned and misaligned waves.

By changing the material's parameters so that the two modes no longer overlap, Padilla and Fan were able to show it could easily become just like the CPAs currently in the literature, but with much more versatility.

"Typical CPAs have only one variable, the material's thickness," said Fan. "We have three: the cylinders' radius, height and periodicity. This gives us a lot more room to tailor these modes and put them in the where we want them, giving us a lot of flexibility for tailoring the CPAs."

Researchers discover anti-laser masquerading as perfect absorber
Traditional 'reverse lasers' can only absorb energy when the incoming electromagnetic waves are perfectly aligned, as in the top example. Credit: Duke University

In the paper, the researchers show that their device can switch between absorbing all phases of electromagnetic waves and only those in sync with one another merely by increasing the height of the cylinders from 1.1 millimeters to 1.4. With this ease of transition, they believe it should be possible to engineer a material that can dynamically switch between the two.

"We haven't done that yet," said Padilla. "It is challenging, but it's on our agenda."

While there aren't currently any devices that make use of the abilities of CPAs, Padilla and Fan have a few in mind. In principle, researchers could engineer a device that measures not just the intensity of incoming light like a normal camera, but also its phase.

"If you're trying to figure out the properties of a material, the more measurements you have, the more you can understand about the material," said Padilla. "And while coherent detectors do exist—we have one in our own lab, actually—they're extremely expensive to build through other technologies."

Explore further: Metal-free metamaterial can be swiftly tuned to create changing electromagnetic effects

More information: Jonathan Y. Suen et al, A Zero-Rank, Maximum Nullity Perfect Electromagnetic Wave Absorber, Advanced Optical Materials (2019). DOI: 10.1002/adom.201801632

Related Stories

Absorbing electromagnetic energy while avoiding the heat

January 27, 2017

Electrical engineers at Duke University have created the world's first electromagnetic metamaterial made without any metal. The device's ability to absorb electromagnetic energy without heating up has direct applications ...

New Metamaterial a 'Perfect' Absorber of Light

June 3, 2008

A team of scientists from Boston College and Duke University has developed a highly-engineered metamaterial capable of absorbing all of the light that strikes it – to a scientific standard of perfection – they report ...

Team develops new metamaterial device

February 24, 2009

An engineered metamaterial proved it can function as a state-of-the-art device in the complex terahertz range of the electromagnetic spectrum, setting a standard of performance for modulating tiny waves of radiation, according ...

Recommended for you

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

How heavy elements come about in the universe

March 19, 2019

Heavy elements are produced during stellar explosion or on the surfaces of neutron stars through the capture of hydrogen nuclei (protons). This occurs at extremely high temperatures, but at relatively low energies. An international ...

Trembling aspen leaves could save future Mars rovers

March 18, 2019

Researchers at the University of Warwick have been inspired by the unique movement of trembling aspen leaves, to devise an energy harvesting mechanism that could power weather sensors in hostile environments and could even ...

Quantum sensing method measures minuscule magnetic fields

March 15, 2019

A new way of measuring atomic-scale magnetic fields with great precision, not only up and down but sideways as well, has been developed by researchers at MIT. The new tool could be useful in applications as diverse as mapping ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Osiris1
not rated yet Feb 15, 2019
Shields up.....red alert!?
Jeffhans1
not rated yet Feb 15, 2019
Power through fiber optics?

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.