The direct conversion of broadband solar radiation into highly coherent laser radiation has attracted scientific and practical interest in recent years. [1] After the first demonstration of a solar-pumped laser (SPL) in 1963, [2] subsequent studies were focused on improving the laser medium and the solar collector design, thereby achieving state-of-the-art high-power SPLs with solar collecting efficiency of up to 32.5 W m À2 (laser output power per unit area of the solar collector optics). [3,

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... ] ] [20] Despite the range of potential applications, the utilization of highly concentrated sunlight has severely restricted the practical applications of SPLs owing to their dependence on an accurate solar tracking system. [21] Further, only the direct components of sunlight can be harvested by concentrating optical elements, such as lenses or mirrors; they do not function efficiently under cloudy conditions when the diffuse component of sunlight is high. Regarding locations, including Susono (Japan) and Karlsruhe (Germany), diffuse horizontal solar radiation represents %49% of the total terrestrial sunlight averagely received annually. [22] 25] Although SPLs, which do not require a mirror/lens-based concentrator system, have been studied for a long time since their introduction in 1983, [26] the technology was only demonstrated T. Masuda Carbon Neutral development division Toyota Motor Corporation