Float zone growth of rare-earth doped lutetium orthovanadate single crystals as new solid state laser materials

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15550169
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Inorganic industrial materials
• Research Institution: HOKKAIDO UNIVERSITY
• Principal Investigator: HIGUCHI Mikio Hokkaido Univ., Grad.School of Eng., Inst., 大学院・工学研究科, 助手 (40198990)
• Co-Investigator(Kenkyū-buntansha): WADA Satoshi The Institute of Physical and Cynical Research, Solid State Optical Science Research Unit, Unit Leader, 固体光学デバイス研究ユニット, ユニットリーダー (90261164)
• Project Period (FY): 2003 – 2004
• Keywords: Floating zone method / Lutetium orthovanadate / Single crystal / Solid state laser / Rare-earth doping / Laser-diode pumping

Research Abstract

Neodymium-doped lutetium orthovanadate (Nd : LuVO_4) has larger absorption and emission cross sections as compared with conventional Nd-doped rare earth orthovanadates and is expected to be applied for laser-diode pumped solid state lasers. LuVO_4 is also expected to be a good host crystal for Tm and Yb, since the tonic radius of Lu^<3+> is comparable to those of Tm^<3+> and Yb^<3+>. In this study, the growth technique of rare-earth (Nd, Tm and Yb) doped LuVO_4 single crystals by the floating zone technique has been established and some spectroscopic properties as a laser material have been investigated.
Each dopant was added with 0.5-4 at% with respect to Lu. Growth conditions were as follows : traveling rate of the molten zone was 20-40 mm/h ; rotation rate was 30-40 rpm ; direction was [110] and atmosphere was an oxygen flow Any as-grown crystal was colored in yellowish ocher, but the coloring was completely eliminated by annealing at 1000 ℃ for 20h in air. Polarizing microscopy proved that the grown crystals contained no macroscopic defects but growth striations were observed only in Nd-doped crystals. Effective segregation efficient was determined to be close to unity for Tm and Yb and about 0.5 for Nd. At this stage, single crystals 5 mm in diameter and 50 mm long have been grown reproducibly for Tm-and Yb-doping of up to 5 at% and Nd-doping of up to 1 at%.
The absorption coefficient of Nd : LuVO_4 was 1.4 times as high as those of other rare-earth orthovanadates. The Nd : LuVO_4 (1 at%) single crystal exhibited excellent laser performance with 880 nm pumping ; that is, the slope efficiency was 73 % and the threshold was 7 mW. Although the laser oscillation experiments for Tm and Yb-doped crystals are underway, it is expected that those crystals also exhibit good laser performance on the basis of their excellent spectroscopic properties.