It is with great sadness and heavy heart that we inform you of the passing of Prof. Toshitaka Idehara on March 18, 2022, at the age of 81. He is the founder and the first director of Research Center for Development of Far-Infrared Region, University of Fukui (FIR UF) and professor emeritus of University of Fukui.

Prof. Toshitaka Idehara graduated from Kyoto University in 1963 and received his Master and Doctoral degrees in Science in 1965 and 1968, respectively, also from the same university. He started his career as a lecturer in the Faculty of Engineering, Fukui University (now University of Fukui) from 1968.  In the early time of his research (1963-1980), he studied negative absorption phenomena in plasma and the instability in electron beam-plasma system. From around 1980, he started researches on development of high-power millimeter and terahertz wave sources based on vacuum electronics and their applications to material sciences and various scientific researches. He is a pioneer in the development of high-frequency gyrotron. After the foundation of FIR UF in 1999, a series of various types of sub-THz gyrotron (FU series and FU CW series) were developed and were used for various scientific researches.  One milestone was the achieved second-harmonic oscillations at more than 1 THz in 2005. Examples of the research subjects using his developed gyrotrons are electron spin resonance (ESR) spectroscopy, dynamic nuclear polarization-nuclear magnetic resonance (DNP-NMR) spectroscopy, X-ray detected magnetic resonance (XDMR) spectroscopy, direct measurement of hyperfine splitting of positronium, light emission from semiconductors and cancer therapy. 

He served as the Editor-in-Chief of International Journal of Infrared and Millimeter Waves (Journal of Infrared, Millimeter, and Terahertz Waves) from 2004 to 2010.  From 2011, he is the Editor-in-Chief Emeritus together with Kenneth J. Button.   He was an active member of board of directors (2010-2018) and Councilor (2019-2021) of Terahertz Technology Forum, Japan.  He was also a member of the 182nd Committee on Terahertz Science, Technology and Industrial Development, Japan Society for the Promotion of Science (2008 -2018). He has hosted IRMMW-THz 2018 conference in Nagoya as the Co-Chair.  He won Science and Technology Award from Minister of Education, Culture, Sports, Science and Technology (MEXT) of Japan in 2009 for the work  “Study on High Power THz Radiation Sources –High Harmonic Gyrotrons.”  He received Fukui Prefectural Academic Grand Prize of Science from the Governor of Fukui Prefecture for the work “Development of High Power Terahertz Radiation Sources –Gyrotrons and their Applications to Terahertz Technologies.” in 2010. He was also awarded Kenneth J. Button Prize with the outstanding contribution to science of infrared, millimeter and terahertz waves, in the 41st International Conference on Infrared, Millimeter and Terahertz Waves, Copenhagen, September 25-30, 2016. Recently, in 2020, he was awarded the Order of the Sacred Treasure, Gold Rays with Neck Ribbon, from the Japanese Government.

He was a great scientist and at the same time a wonderful person, with a bright, upright and kind personality. Many students and researchers trust him and gather around him. Therefore, he had many friends not only in Japan but all over the world. Even now, researchers from around the world visit, stay and carry out active researches at FIR UF, which he founded.

Prof. Idehara, a beloved and cherished mentor, colleague and friend, will be greatly missed by many, but never will be forgotten.

Prof. Masahiko Tani
Prof. Yoshinori Tatematsu
Prof. Seitaro Mitsudo

Research Center for Development of Far-Infrared
University of Fukui
Fukui, 910-8507, Japan

March 28, 2022