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Researchers at North Carolina State University have successfully “squeezed” infrared light down to 10 percent of its wavelength while preserving its frequency.
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This breakthrough was achieved using a thin strontium titanate membrane and the phono polaritons it produced after using near-field synchrotron spectroscopy.
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This thin film could lead to a range of new infrared imaging devices and other thermal management systems – potentially releasing heat by converting it to infrared light.
The human eye is a natural wonder, the result of millions of years of evolutionary tinkering and… remarkably restrictive. Our eyes can only see a tiny bit of the electromagnetic spectrum, so seeing anything else requires relying on technology that can spot these “invisible” wavelengths.
One of the most useful wavelengths is infrared, whose waves extend between 760 nanometers and 100,000 nanometers (the name comes from the fact that it is just longer than the color red, the longest wavelength in the visible spectrum). Infrared is used in all kinds of applications – especially imaging – and being able to manipulate this wavelength can produce better results.
That’s why scientists at North Carolina State University successfully “squeezed” infrared light to 10 percent of its wavelength while maintaining its frequency. The researchers achieved this breakthrough by using a special class of oxide membranes rather than bulk crystals, which traditionally can only barely press the infrared light. The results of this study were published earlier this month in magazine The nature of communication.
“We have shown that we can limit infrared light to 10% of its wavelength while maintaining its frequency – meaning the time it takes for a wavelength to cycle is the same, but the distance between the peaks of the wave is much closer together,” Yin Liu , co-author of the study, said in a press statement. “Bulk crystal techniques limit infrared light to about 97% of its wavelength.”
According to the statement, the researchers used “transition metal perovskite materials” in the study. Using pulsed laser deposition—which involves a powerful pulsed laser beam in a vacuum chamber—the researchers grew a 100-nanometer-thick membrane made of strontium oxide and titanium called strontium titanate (SrTiO3). Once completed with very few defects, the films were removed from this substrate and placed on a silicon substrate.
To test this new device and see if it could “squeeze” infrared light to a useful degree—an idea that the researchers say was only theoretical—the team turned to the Advanced Light Source at Lawrence Berkeley National Laboratory. He operates this research facility infrared program capable of investigating materials at the micro- and nanoscale. The team performed near-field synchrotron spectroscopy on a thin film of strontium titanate, and what was once theoretical became very practical.
Understanding what happened next requires a brief foray into particle physics 101. Photons are particles of light and the basic unit of the electromagnetic spectrum. Phonons, on the other hand, are “a fancy word for a particle of heat” (according to MIT), but can also be thought of as sound energy. Both photons and phonons deal in the realm of excitations and vibrations – however, when an infrared photon is coupled with an optical phonon (aka a phonon that can emit or absorb light), then they form a quasiparticle called a “phonon polariton”. ” It’s these polaritons that squeeze.
“Theoretical papers proposed the idea that transition metal perovskite oxide membranes would allow phonon polaritons to confine infrared light,” Liu said. “And our work now shows that phonon polaritons confine photons and also prevent photons from propagating beyond the surface of the material.”
Liu and his colleagues said the breakthrough could lead to a whole new generation of infrared imaging technology and temperature control devices. “Imagine,” Liu said, “that you could design computer chips that could use these materials to dissipate heat by converting it to infrared light.”
Well, thanks to this breakthrough, we may not have to imagine for long.
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