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Recently, the scientists have revealed for the first time in Optica report, “There is a new type of mirror, which functions like no other – it relinquishes a proverbial shiny metallic surface and rather reflects infrared light by using an unusual magnetic property of a non-metallic meat-material.
Researchers are able to incarcerate and harness electromagnetic radiation by placing nano-scale antennas at or very near the surface of these so-called “magnetic mirrors” that evolve enticing potential in new classes of chemical sensors, solar cells, lasers, and other optoelectronic devices.
Michael Sinclair, co-author on the paper and a scientist at Sandia National Laboratories in Albuquerque, New Mexico, USA who co-led a research team with fellow author and Sandia scientist Igal Brener stated that, “We have achieved a new milestone in magnetic mirror technology by experimentally demonstrating this remarkable behavior of light at infrared wavelengths. Our breakthrough comes from using a specially engineered, non-metallic surface studded with nano-scale resonators.”
Based on the element tellurium, these nano-scale cube-shaped resonators are significantly smaller than the width of a human hair and even tinier than the wavelengths of infrared light that is necessary to achieve magnetic-mirror behavior at these incredibly short wavelengths.
Sinclair explained, “When it comes to the size and shape of these resonators, they are critical as their magnetic and electrical properties that enable them to intermingle distinctively with light, scattering it across a specific range of wavelengths to produce a magnetic mirror effect.”
Early Magnetic Mirror Designs
When it comes to the traditional mirrors, they have the ability to reflect light by interacting with the electrical component of electromagnetic radiation. Due to this, though, they do more than reverse the image; they also reverse light’s electrical field eventually causing no impact on the human eye. But, it does have major implications in physics, particularly at the point of reflection where the opposite incoming and outgoing electrical fields produce a canceling effect. Due to the temporary squelching of light’s electrical properties, it prevents components like nano-scale antennas and quantum dots from interacting with light at the mirror’s surface.
In contrast, a magnetic mirror has the ability to reflect light by interacting with its magnetic field, preserving its original electrical properties. Brener stated that, “A magnetic mirror, thus, develops a very strong electric field at the mirror surface, enabling maximum absorption of the electromagnetic wave energy and paving the way for exciting new applications.”
Though, unlike silver and other metals, there is no natural material that got the ability to reflect light magnetically. Magnetic fields can reflect and even bottle-up charged particles like electrons and protons. But photons, which have no charge, pass through freely.
Brener added, “Nature doesn’t provide a way to magnetically reflect light. Thus, scientists, are producing meta-materials (materials not found in nature, engineered with specific properties) that has the ability to create the magnetic-mirror effect.
At first, this could only be achieved at long microwave frequencies that will allow only a few applications like microwave antennas.
Some other researchers have recently achieved limited success at shorter wavelengths using “fish-scale” shaped metallic components. Though, these designs, faced substantial loss of signal, along with an uneven response due to their particular shapes.
Mirrors Without Metals
In order to overcome these implications, the team of researchers developed a specially engineered two-dimensional array of non-metallic dielectric resonators (nano-scale structures) that robustly interrelate with the magnetic component of incoming light. Over the former designs, these resonators have a number of important advantages.
Initially, tellurium, a dielectric material used, has much lower signal loss than metals do, making the new design much more reflective at infrared wavelengths and developing a much stronger electric field at the mirror’s surface. Secondly, the standard deposition-lithography and etching processes were used to manufacture nano-scale resonators that are already widely used in industry.
When it comes to the reflective properties of the resonators, they emerge because they behave, in some respects similar to the artificial atoms, first absorbing and then re-emitting photons. On the other hand, atoms naturally do this by absorbing photons with their outer electrons and then re-emitting the photons in random directions. This is the way how atmospheric molecules scatter specific wavelengths of light, causing the sky to appear blue during the day and red at sunrise and sunset.
The meta–materials in the resonators achieve a similar effect, but absorb and re-emit photons without reversing their electric fields.
Proof of the Process
In order to confirm that the researchers design was actually behaving like a magnetic mirror needs exquisite measurements of how the light waves overlap as they pass each other coming in and reflecting off of the mirror surface. As, on reflection, normal mirrors reverse the phase of light, proof that the phase signature of the wave was not reversed would be the “smoking gun” that the sample was behaving as a true magnetic mirror.
In order to detect this, the Sandia team used a technique dubbed as time-domain spectroscopy that has been widely used to measure phase at longer terahertz wavelengths. Only some groups in the world have revealed this technique at shorter wavelengths (less than 10 microns), researchers stated. This technique has the ability to map both the amplitude and phase information of a light’s electric field.
Sheng Liu, Sandia postdoctoral associate and lead author on the Optica study stated that, “The results of the study clearly indicates that there was no phase reversal of the light. This was the ultimate revelation that this patterned surface behaves like an optical magnetic mirror.”