SPECTROSCOPY: Compact magnets provide terahertz light

May 1, 2000
TOKYO?Researchers at Jasco Corp. and the Institute for Molecular Science (Okazaki) have jointly developed a compact, high-power spectroscopy system that uses a terahertz light source

Incorporating news from O plus E magazine, Tokyo

TOKYO—Researchers at Jasco Corp. and the Institute for Molecular Science (Okazaki) have jointly developed a compact, high-power spectroscopy system that uses a terahertz light source (see photo on p. 94). The system has become a key part of a collaborative research project with a group at Kobe University (Kobe), where the instrument has been used to do spectroscopic studies of protein solutions in the terahertz region—a previously difficult task.

In the system, terahertz light is produced by applying a pulse of light from an ultrafast laser on an indium arsenide semiconductor surface placed in a strong magnetic field. For a field with strength of 2 Tesla (T), the device emits terahertz light with power approaching 1 mW—four orders of magnitude greater than what has been achieved in the past.

High-power terahertz light source allows a spectroscopic system to analyze materials with very high absorption coefficients in the terahertz region (white area top right is an aperture block made of paper).
Click here to enlarge image

Such strong magnetic fields are typically created using electromagnets that need cooling devices, which take up a lot of space. The group approached Sumitomo Special Metals Co. Ltd. (Osaka) to see if the company could make a permanent magnet capable of producing a 2-T field. Sumitomo developed a magnetic circuit that can produce 2-T fields in select areas using multiple neodymium-iron-boron permanent magnets. The group uses a compact femtosecond fiber laser as the ultrafast light source.

The result is a compact and easy-to-use terahertz spectroscopic system. The group's goal was to develop a system that could be used by researchers who have no special knowledge in fields such as laser technology. Jasco plans to commercialize the product in two or three years and aims to reduce the size of the system to approximately 300 x 420 mm.

Protein-solution spectroscopy

The Kobe University group has used this device to do spectroscopy of protein solutions. Proteins consist of very long polymers that are folded in a particular state when they are in a solvent. The folding is induced by intramolecular forces, as well as by the forces between the molecules and solvent, but the details of how it reaches its final state are shrouded in mystery. It is thought that diseases such as mad-cow disease and Alzheimer's disease might be caused by proteins that have folded in a way different from that of the normal protein, thus losing chemical functionality. The protein-folding problem is indeed a large one in the field of biochemistry.

By performing terahertz spectroscopy on protein solutions, the structure and functionality of these proteins can be clarified. However, because water absorbs terahertz light efficiently, light sources with very high power are necessary. The new terahertz light source has resulted in the successful recording of the absorption spectrum of protein solutions. Analysis of the data is ongoing.

Courtesy O plus E magazine, Tokyo

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