Solar-pumped solid state lasers are one of the promising systems to utilize the solar energy. In previous studies, Cr,Nd:YAG has been used as a gain medium; however, its spectral properties are not sufficient for efficient energy conversion. Nd:YVO₄ is known as an excellent gain medium for Nd-lasers because of excellent optical properties. In this study, we grew Cr,Nd:YVO₄ single crystals by the floating zone method and investigated their spectral properties.

A ceramic feed rod was prepared with a composition of Y_1-x-yCr_xNd_yVO₄ where x=0.005-0.02 and Y=0.25-2. Single crystals were grown under conditions of growth rate: 10-20 mm/h, seed orientation: [110], atmosphere: air or O₂/N₂ mixed gas.

When the growth rate was 20 mm/h, the grown crystals showed green gradation parallel to the growth direction. Little gradation was observed for the crystal grown at 10 mm/h, but the green color was not so deep. These results imply that segregation and evaporation of Cr-component simultaneously occur during crystal growth. The most effective way to obtain a crystal with homogeneous Cr-concentration was to prolong the growth length more than 40 mm.

Cr,Nd:YVO₄ showed strong absorption in the wavelength region of 350-500 nm. Although the peak wavelength of 400 nm does not correspond to the solar radiation peak, the absorption coefficient of Cr,Nd:YVO₄ is significantly large in despite of relatively low Cr-concentration of less than 1 at%. The absorption cross section of Cr,Nd:YVO₄ at 430 nm, where Cr,Nd:YAG has the maximum absorption is about 33´10^-20 cm², which is 4.7 times as large as that of Cr,Nd:YAG. By pumping at 400 nm, Cr,Nd:YVO₄ showed strong fluorescence band around 900 nm and 1060 nm by Nd³⁺. No fluorescence band of Cr³⁺ was observed in the visible region, which implies that most of the energy absorbed by Cr³⁺ is effectively transferred to Nd³⁺. These results demonstrate that Cr,Nd:YVO₄ single crystals are one of the promising materials for solar-pumped solid state laser systems.

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1. Float zone growth and spectral properties of Cr,Nd:CaREAlO₄ (RE=Y, Gd) single crystals for potential use in solar-pumped solid state lasers
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