Development of ultra-highly precise terahertz measurement technology

The Watanabe Group in Keio University’s Department of Physics utilizes light to understand the micro-scale properties of materials. The Group also does R&D aiming to create new material states using light. One topic the Group focuses on is material science using terahertz waves.
Terahertz waves have low frequency, one-hundredth to one-thousandth that of visible light. Their particular energy makes them suitable for investigating and manipulating phenomena on new energy scales. Many such phenomena occur in materials that are still difficult to understand, from quantum nano-materials to superconductors, and even biological molecules.
The Watanabe Group aims to develop ultra-high-precision technology for measuring terahertz wave amplitude, phase, polarization, and frequency. By using this technology to observe and manipulate materials, the Group hopes to take the lead in next-generation materials science.

Q. We noticed that terahertz waves are very “simple” waves. Light possesses the basic properties of amplitude, phase, and polarization. In particular, we’ve been measuring terahertz wave polarization states with very high precision, with the aim of enabling scientific and industrial applications for terahertz waves. What we do in the industrial applications is, we investigate the height of objects from polarization angles, which is a very new, globally pioneering method. We’re developing technology for using this method to identify differences in surface height below one micron, which is extremely high resolution for long-wave terahertz waves.

Terahertz waves are topical as an alternative to high-energy X-rays for non-destructive inspection. There are high hopes that terahertz waves can also be used to observe the interior of materials, where visible light can’t penetrate. The Group is also doing R&D aiming to induce large changes in material properties, such as phase transitions, through terahertz pulse excitation.

The Watanabe Group is also doing research on nanoscale materials science. This research involves observations using an ultra-short pulse laser, with pulse width of about 100 fs, as the light source. By developing measurement methods with even higher precision using light, the researchers are working hard to understand new properties and phenomena, such as the behavior of electrons and spins in materials.

Q. There are still a great many properties of materials that aren’t well-understood. I think it’s very important to clarify those unknown properties and make them useful. What we’re working on now is high-precision measurement. By revealing what actually happens inside materials, we’d like to contribute to society — for example, by discovering new material functions, or proactively utilizing light to create new functions.

The Watanabe Group manipulates light freely, working to understand entirely new properties of materials.
The researchers will continue investigating new possibilities, looking for new ways to utilize light.
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