Solar-pumped lasers have recently been attracted much attention from the viewpoint of suitable energy development. In previous studies, Cr,Nd:CaREAlO₄was developed as a host crystal for the Nd-lasers, but there have no reports on the crystal growth and spectral properties of Cr- and Nd-codoped CaREAlO₄. Since CaREAlO₄ does not have any tetrahedral site, spectral drawbacks found in YAG may be improved. In this study, we grew Cr,Nd:CaREAlO₄(RE=Y, Gd) single crystals by the floating zone method and investigated their spectral properties.

   A ceramic feed rod with a composition of CaRE_1-xNd_xAl_0.999Cr_0.001O₄where x=0-0.01 was used for the single crystal growth by the floating zone method. Crystals were grown with conditions of growth rate: 2.5-5mm/h, atmosphere: air, CO₂ or O₂, rotation rate: 30-60 rpm.

   The grown single crystals were transparent and deep red in whole. A lower growth rate of 2.5 mm/h and a higher rotation rate of 60 rpm were effective to suppress the formation of voids.

   Cr,Nd:CaYAlO₄showed strong absorption in the wavelength region of 320-600 nm. The absorption cross section of σ-polarization at 430 nm, where Cr,Nd:YAG has the maximum absorption, is about 862 ×10^-20 cm², which is 120 times as large as that of Cr,Nd:YAG. Cr,Nd:CaGdAlO₄ also showed strong absorption in the wavelength region of 340-600 nm. Although the absorption cross section of Cr,Nd:CaGdAlO₄ was less than that of Cr,Nd:CaYAlO₄, the absorption peak was shifted to the longer wavelength of 470 nm. By pumping at 400 nm, Cr,Nd:CaYAlO₄ showed strong fluorescence bands around 900 nm and 1080 nm by Nd³⁺. This result indicates that the energy absorbed by Cr³⁺ is effectively transferred for Nd³⁺in these crystals, and Cr,Nd:CaREAlO₄single crystals are therefore 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:YVO₄ single crystals for potential use in solar-pumped solid state lasers
2. Dielectric permittivity mappings obtained by GHz region Microwave Microscopy using non-contact probe and their noise reduction of Fourier transform refinements