As announced the other day, the 2018 Nobel Prize in Physics was given for the development of optical tweezers and ultrashort pulse lasers. Optical technology is constantly advancing and penetrating into various industrial fields. Recently, the power of fiber lasers is remarkably increasing, and therefore, it becomes a promising processing tool for metalworking and its marketing value is also increasing. In addition, now we already have many processes that cannot be done without laser, and this trend will continue in the future. However, we often hear from potential users of optical technology who work at machining, "I understand the importance of optical technology, but I am hesitating to introduce because I do not know how to use". This is the same from the actual feeling as an optical researcher of me, and I feel the lack of optical engineers who realize new technological ideas. In other words, the current state of the industry is in short supply of optical engineers. As a factor of short supply of optical engineers, mostly optical education is often in charge of the Department of Electrical and Electronic Engineering, Faculty of Engineering at Japanese universities, and therefore, most of the students that have learnt optics are employed as electrical/electronic engineers after graduation. Meanwhile, it is also true that efforts to resolve at various universities have begun. While introducing our optical education (student experiment: Control of polarization state), we will examine optical education at university and its role for the optical industry.
The time-resolved photoluminescence of free and bound excitons in bulk single-crystal CuInS2 grown by the traveling heater method is examined. It is found that radiative decay of the free exciton at 1.535 eV and the bound exciton at 1.530 eV is exponential with two characteristic decay-times while that of the bound excitons at 1.525 and 1.520 eV is well-represented by a single exponent at low temperatures. The radiative lifetimes of the free exciton and the bound excitons at 1.530, 1.525, and 1.520 eV are obtained to be 320 ps, 500 ps, 2.1 ns, and 3.5 ns, respectively. A thermal release process of the observed bound excitons is discussed in terms of the obtained activation energy. The capture center cross-section for free exciton is also estimated. According to our estimates, a neutral charge is to be assigned to the defect centers associated with the observed bound excitons.