Researchers develop new technology to leverage mid- and far-infrared light

The electromagnetic spectrum encompasses far more than just visible light. Beyond what the human eye can perceive, there lies a vast range of frequencies with significant technological potential. Scientists at Rice University have devised a groundbreaking plan to tap into an unexplored segment of this spectrum.

This untapped region exists in the mid- and far-infrared light range, encompassing frequencies of 5-15 terahertz and wavelengths ranging from 20-60 micrometers. Surprisingly, this part of the spectrum lacks robust commercial products, unlike the well-developed technologies found in higher optical frequencies and lower radio frequencies.

Leading the charge in this research is Rui Xu, a third-year doctoral student at Rice University. Alongside Xu, Hanyu Zhu, the William Marsh Rice Chair and assistant professor of materials science and nanoengineering, plays a pivotal role in the Emerging Quantum and Ultrafast Materials Laboratory, where these exciting experiments take place.

Their work, recently published in Advanced Materials, promises to unlock the potential of the mid- and far-infrared light range, opening doors to innovative technologies that were previously beyond our reach. From enhanced communication systems to advanced medical imaging, the possibilities are vast and exciting.

Pictured are three samples of ultrafast terahertz field concentrators fabricated by graduate student Rui Xu in Rice University's Emerging Quantum and Ultrafast Materials Laboratory. The bottom layers (visible as a white squares) are made of strontium titanate with concentrator structures  microscopic arrays of concentric rings that concentrate terahertz frequencies of infrared light  patterned on their surfaces. The arrays are visible with a microscope (inset) but have the appearance of a fine-grained pattern of dots when viewed with the naked eye. Credit: Gustavo Raskosky/added inset by Rui Xu/Rice University

In the quest to explore the “new terahertz gap,” an elusive frequency region within the electromagnetic spectrum, researchers have uncovered a promising avenue for advancing quantum electronics and medical diagnostics. This frequency range, spanning 5-15 terahertz, has remained challenging to access due to the strong interaction between light and most materials, causing rapid absorption.

However, a team of researchers, led by Hanyu Zhu from Rice University, has found a solution using a material called strontium titanate. This oxide of strontium and titanium exhibits a remarkable property known as quantum paraelectricity, where its atoms display significant quantum fluctuations and vibrate randomly. This unique behavior allows it to couple strongly with terahertz light, forming particles called phonon-polaritons, which remain confined to the material's surface without getting lost inside it.

The researchers demonstrated the effectiveness of strontium titanate phonon-polariton devices in the 7-13 terahertz frequency range by designing and fabricating ultrafast field concentrators. These devices can compress light pulses into a volume smaller than the wavelength of light while maintaining their short duration, resulting in an incredibly powerful transient electric field of nearly a gigavolt per meter.

The strength of this electric field enables intriguing applications, such as changing the structure of materials to create new electronic properties and generating a new nonlinear optical response from trace amounts of specific . These responses can be detected using a common optical microscope, making it a potential game-changer for medical diagnosis.

The research team's design and fabrication methodology are not limited to strontium titanate but can be applied to various commercially available materials, potentially enabling photonic devices across the broader 3-19 terahertz range.

The study involved contributions from several researchers, including Xiaotong Chen, Elizabeth Blackert, Tong Lin, Jiaming Luo, Alyssa Moon, and Khalil JeBailey, each adding valuable insights and expertise to this groundbreaking endeavor.

Source: Rice University

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