Akiyoshi Mitsuishi was born on October 15, 1925, in Taejon, South Korea. He spent his childhood and early life in Taejon, and spent high school life in Hiroshima, Japan. Then he went to Kyoto to study at Kyoto University. He received an undergraduate degree in 1948. He continued his graduate studies at Kyoto University. During the period he was particularly affected by Prof. Uchida in spectroscopy and by Prof. Yukawa, the first Nobel Prize Winner of Japan in theoretical physics. Mitsuishi joined the research staff of Osaka University in 1940, where he mainly studied the optical properties of solids working in Prof. Yoshinaga’s laboratory. Akiyoshi contributed largely to the construction of the famous Far Infrared (FIR) grating spectrometer of Osaka University. His important role was to develop optical components such as the pile-of-plates polarizer, alkali halide powder filters (so-called Yoshinaga filters) and woven metal mesh reflection filters. Yoshinaga filters are particularly useful for suppressing the higher orders of the grating and useful as cooled filters for cooled detectors. At the initial stage of FIR spectroscopy by use of this grating spectrometer, Mitsuishi and collaborators applied it to the measurements of reststrahlen bands of well-known NaCl, KCl, and KBr, at 100 K, 200 K and 300 K. He and collaborators realized that NaCl has another subpeak and KBr has also a small subpeak on the sharp rise of short wavelength side (1959) in addition to the measured results in 1930. Charles Kittel included that data in a revision of his world-famous text book ‘Introduction to Solid State Physics’. This made Mitsuishi famous world-wide. In succession he pushed forward to the study of material science in solids such as color centers in alkali halides, phase change of ferroelectric crystals, shallow impurity levels of the doped semiconductor, and localized impurity modes. His scientific activities are written in Invited Review Articles of Journal of Infrared, Millimeter, and Terahertz Waves Vol. 35 (2014) and in Infrared and Millimeter Waves (ed. K. J. Button) 16, Chap. 6 (1986).

Akiyoshi was willing to support our communities which are not only domestic but international. He was the President of a large academic community Applied Physics in Japan and in succession was a member of the most powerful academic organization, the Science Council of Japan. He was the first president of The Japan Society of Infrared Science and Technology. Internationally he was an honorable advisor of the British journal Infrared Physics and the international advisor of the Chinese journal Infrared Research.

Akiyoshi supported our conference series working as the Local Committee Chair of the Takarazuka Conference in 1984, Vice Chair of the Sendai Conference in 1994 and Honorary Chair of the Otsu Conference in 2003. He was really a great scientist and a broad-minded person.

Akiyoshi Mitsuishi was awarded ‘The Order of the Sacred Treasure, Gold Rays with Neck Ribbon’ by the Emperor as a Great Professor.

Kiyomi Sakai October 4, 2020
Research Center for Development of Far-Infrared Region
University of Fukui
Fukui, Japan