2023-07-09 19:10:00
RIKEN scientists have successfully exploited the terahertz band of the electromagnetic spectrum with new hand-sized devices that can perform ‘x-rays’ without the use of ionizing radiation.
Several technologies – from smartphones to infrared telescopes in the James Webb Space Telescope, to high-speed wireless telecommunications devices using microwaves – exploit sections of the electromagnetic spectrum.
However, between commonly used microwaves and infrared light lies a neglected region called the terahertz band. Terahertz waves have many potentially exciting applications, as they can be used to see through or into materials similar to X-rays. However, unlike X-rays, terahertz waves do not emit ionizing radiation which can be harmful in the long term.
Technological challenges of the terahertz spectrum
The implementation of terahertz technologies has been hampered so far due to the difficulty of adapting microwave or visible light technologies to the terahertz range in useful formats and at sufficient output powers. For example, one approach to generating terahertz waves has been to develop electrical devices that produce high frequency, very short wavelength microwaves.
However, this has been difficult in part because these devices require highly optimized parameters to produce better electrical performance, which has proven to be a challenge.
Another strategy is to produce terahertz waves by converting shorter, higher frequency waves of infrared light, using materials known as nonlinear crystals. At the RIKEN Center for Advanced Photonics, this second strategy is being explored – producing terahertz waves by converting the output of an infrared laser.THE AWAKENING MIND: Located between microwaves and infrared radiation on the electromagnetic spectrum, the terahertz interval has been underutilized in technology so far. Like X-rays, terahertz waves have the ability to see through materials. But since terahertz waves have much lower frequencies (and therefore energies) than X-rays, they do not pose the same health risk as ionizing radiation. 2023 RIKEN
The crucial role of hand-sized devices
The THE KINGDOM focused on the use of lithium niobate, a nonlinear crystal that produces a beam of terahertz waves when irradiated with near-infrared laser light. These researchers have recently made significant progress towards this goal and have several ongoing industrial collaborations.
They managed to further miniaturize their terahertz wave source by replacing the lithium niobate crystal they previously used with a thin lithium niobate crystal with an artificially polarized modulated microstructure, called a periodically polarized lithium niobate crystal. (PPLN).
Industrial and research impact
Additionally, these highly miniaturized, high-power terahertz wave systems are complemented by recent developments in compact and powerful photonic lasers. These devices use a new on-chip laser that produces far-infrared laser pulses at sub-nanosecond speeds and high powers.
Currently, industrial collaborations form a key part of their work. The strong sub-terahertz emissions that their devices can generate are particularly suited to imaging and analytical work. They are conducting joint research with Japanese companies specializing in electronics, optics and photonics to develop non-destructive testing applications and terahertz wave spectroscopy equipment.
For a better understanding
1. What is the terahertz spectrum?
The terahertz spectrum refers to the band of the electromagnetic spectrum that lies between microwaves and infrared light. Terahertz waves have many potential applications because they can be used to see through or inside materials in a manner similar to X-rays, without delivering harmful ionizing radiation.
2. What are the challenges of exploiting the terahertz spectrum?
One of the main challenges is the difficulty of adapting microwave or visible light technologies to the terahertz band at useful sizes and powers. Additionally, generating terahertz waves requires highly optimized parameters to produce superior electrical performance, which has proven to be challenging.
3. How did the RIKEN research team overcome these challenges?
The RIKEN research team explored a strategy of producing terahertz waves by converting infrared waves using materials called nonlinear crystals. They succeeded in developing hand-sized devices capable of producing terahertz waves powerful enough for most practical applications.
4. What are the possible applications of terahertz waves?
Terahertz waves can be used in a variety of fields, ranging from medical imaging to security to the analysis of ancient materials. They can reveal the chemical composition of substances through specific absorption patterns, making it easy to identify colorless liquids that look identical to the naked eye, for example. Additionally, they can be used to analyze industrial paints and exterior coatings non-destructively.
5. What distinguishes RIKEN’s work in the field of terahertz waves?
RIKEN’s work is unique in that it has developed hand-sized devices capable of producing powerful terahertz waves, paving the way for practical and portable applications of terahertz technology. In addition, their research relies on a photonic conversion between light waves and terahertz waves, opening new possibilities for quantum research.
Caption for main illustration: device created by Hiroaki Minamide and his team, which efficiently converts infrared radiation into terahertz waves. It can generate terahertz radiation across the entire terahertz band. Credit 2023 RIKEN
About the researcher: Hiroaki Minamide is head of the tera-photonics research team and head of the terahertz research group at RIKEN. He is also a visiting professor at the University of Chiba. He joined RIKEN in 1999 and, following working as a Researcher and Deputy Team Leader, he has worked as a Team Leader since 2010 and as a Group Director since 2020. He completed his undergraduate degree in Communications Engineering , as well as his master’s and doctorate degrees in electrical engineering from Tohoku University, Japan, in 1993, 1996, and 1999, respectively. His research focuses on high-power terahertz wave generation and ultrasensitive terahertz wave detection using nonlinear optics, as well as their unique terahertz applications.
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