Float zone growth and spectral properties of Cr,Nd:CaYAlO4 single crystals

Cr,Nd:CaYAlO4 single crystals were grown by the floating zone method and their spectroscopic properties were investigated. Many voids were observed in the crystals grown with a stoichiometric feed rod even at a relatively low growth rate of 2.5 mm/h, while a void-free crystal was grown at the same growth rate using a feed rod the composition of which was Y-rich to Ca. These results indicate that voids were attributable to constitutional supercooling due to the segregation of main constituents caused by the difference in congruent and stoichiometric compositions. The as-grown crystals were deep red and showed strong absorption in the wavelength region of 320-600 nm. The absorption cross section for σ-polarization at 430 nm, where Cr,Nd:YAG has the maximum absorption, is about 1160×10−20 cm2, which is 165 times as large as that of Cr,Nd:YAG. By pumping at 400 nm, which is a part of the absorption band of Cr3+, Cr,Nd:CaYAlO4 showed fluorescence bands around 900 nm and 1080 nm by Nd3+ indicating energy transfer from Cr3+ to Nd3+ in the crystal. Cr,Nd:CaYAlO4 single crystals are therefore one of the promising gain media for solar-pumped solid state laser systems.