An Essential Keyword for the Research Is “Photo-induced Metallic Structures”
Among the various methods of generating THz waves, Dr. Okada utilizes the method of photo-irradiation of photo-conductive antennas or electro-optic crystals with a femtosecond-pulse laser. A femtosecond-pulse laser has an extremely short pulse width in the scale of 10 to 100 femtoseconds. We need device to promote his research.
The research topic of Dr. Okada's study is “THz sensing technologies”. He uses the attenuated total reflection (ATR) method to measure or modulate THz waves reflected from samples through a prism to determine extremely fine reflective responses. This method was developed by Professor Koichiro Tanaka, a Professor at the Kyoto University Institute for Integrated Cell-Material Sciences. For the measurement, Dr. Okada developed this method using semiconductor prism. The reflection plane of the prism is “excited” with a spatially modulated, femtosecond optical pulsed laser..” When the reflection plane is excited, electrons in the semiconductor prism obtain energy by the optical pumping, which become free -like. Areas where free-like electrons are generated become metallic. Thus, the photo-induced metallic materials or structures possibly emerged by the optical pumping The aim of this research is to sense various types of substances by applying these photo-induced structures to various formats, such as gratings, holes or circles.
Periodic structures in metals are used as optics such as filters in THz frequency regime . Periodic structures created by the photo-induced technique can be utilized as THz filters. Since they are temporal structures, the shape of the structures can be changed easily and reused repeatedly. The ATR technique in combination with photo-induced structures was developed by Dr. Okada. He told us, “THz ATR technique leads us to success by chance.”