New Research


Spectroscopy connecting light and radio wave

Ultrabroadband time domain spectroscopy for infrared light and radio wave

Professor: Masaaki Ashida, Associate Professor: Masaya Nagai, Assistant Professor: Eiichi Matsubara

   Our laboratory is investigating frontier materials using spectroscopy to create novel optical devices. As seen in the above figure, visible light shown with a rainbow is nothing but electromagnetic wave which includes radio wave. Covering very wide frequency region enables us to obtain lots of information on materials.

   Electric field of light can be measured with an antenna, which is popular in radio waves. Here the frequency of light is extremely high if you compare with radio waves, so that ultrashort gate is needed to register the instantaneous value of the electric field. We have already succeeded in the detection of the wave up to 170 THz in frequency, 2μm in wavelength. Unfortunately solid state devices with higher sensitivity inevitably show blind region caused by the absorption of phonons in solids. Recently by using air-plasma created with strong femtosecond light pulses, we successfully generated ultrabroadband infrared pulses covering from sub-THz up to 200 THz. In addition, we achieved direct observation of their electric fields also using air-plasma, shown in the middle figure. The bottom figure shows its Fourier-transformed amplitude spectrum, which extends up to 150 THz. Now we are applying this novel method to various materials, e.g. semiconductors, superconductors, and strongly correlated electron systems. On the other hand, such new methods are applicable to a novel communication technology which bridges conventional microwave or new terahertz communication and optical communication techniques.

Ashida laboratory
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