Researchers from Rice University have identified a previously unused portion of the electromagnetic spectrum that holds great potential for technological advancements. While visible light is well-explored, frequencies beyond human vision have remained largely untapped. This gap, known as the “new terahertz gap,” spans frequencies of 5-15 terahertz and wavelengths ranging from 20-60 micrometers. According to Rui Xu, a lead author on the study, this area lacks commercial products compared to higher optical frequencies and lower radio frequencies. However, the research conducted at Rice University’s Emerging Quantum and Ultrafast Materials Laboratory offers a solution to this problem.
Overcoming the Challenges with Strontium Titanate
One of the main challenges researchers face in this frequency region is finding suitable materials to carry and process light. Most materials strongly interact with light waves in this range and quickly absorb them. However, the research team led by Hanyu Zhu, an assistant professor of materials science and nanoengineering, has found a way to turn this strong interaction to their advantage using strontium titanate.
Strontium titanate, an oxide of strontium and titanium, exhibits a unique property called quantum paraelectricity. This property allows the atoms of the material to couple with terahertz light, forming new particles known as phonon-polaritons. These phonon-polaritons are confined to the surface of the material, preventing them from being lost inside. Unlike other materials that only support phonon-polaritons in a narrow frequency range, strontium titanate works for the entire 5-15 terahertz gap.
By designing and fabricating ultrafast field concentrators, the researchers were able to prove the concept of strontium titanate phonon-polariton devices in the frequency range of 7-13 terahertz. These devices compress the light pulse into a volume smaller than the wavelength of light, maintaining its short duration. This compression results in a strong transient electric field of nearly a gigavolt per meter. Such a powerful electric field can be utilized to change the structure of materials, creating new electronic properties. It can also generate a new nonlinear optical response from trace amounts of specific molecules, which can be detected using a common optical microscope.
The design and fabrication methodology developed by Zhu’s group have broad applicability, extending to many commercially available materials. This breakthrough could potentially enable the development of photonic devices in the 3-19 terahertz range.
In addition to Xu and Zhu, other contributors to this research include Xiaotong Chen, a postdoctoral researcher in materials science and nanoengineering; Elizabeth Blackert and Tong Lin, doctoral students in materials science and nanoengineering; Jiaming Luo, a doctoral student in applied physics; Alyssa Moon, a former undergraduate student at Rice University; and Khalil JeBailey, a senior in materials science and nanoengineering at Rice.
The groundbreaking research conducted at Rice University has unlocked the potential of the “new terahertz gap” in the electromagnetic spectrum. By leveraging the unique properties of strontium titanate, the researchers have paved the way for the development of new photonic devices and the study of quantum materials. This discovery holds promising implications for various fields, including quantum electronics and medical diagnosis.
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