Float zone growth of thulium-doped rare-earth orthovanadate single crystals for eye-safe lasers

用于人眼安全激光器的掺铥稀土原钒酸盐单晶的浮区生长

• 批准号: 13650888
• 负责人: HIGUCHI Mikio
• 金额: $ 2.37万
• 依托单位: HOKKAIDO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650888/
• 关键词: eye-safe laser; rare-each orthovanadate; single crystal; floating zone method; thulium doping; spectroscopic properties; レーザ結晶; アイセーフ; ツリウム

The demand for eye-safe lasers has been increasing in the field of lidar sensing and medical applications. Thulium (Tm)-doped crystals are one of the promising materials for the eye-safe lasers because they can easily be pumped usuing laser-diode. As a host crystal of the Tm-lasers, GdVO_4 single crystals are superior to other crystals such as YAG and fluorite from the viewpoints of thermal conductivity and absorption coefficient. In this study, float zone growth of Tm-doped GdVO_4 single crystals were tried and their spectroscopic properties were investigated.Transparent, crack-free Tm : GdVO_4 single crystals were successfully grown by the floating zone method using an pure oxygen flow as a growth atmosphere. Tm-doping of up to 20 at% was possible at a high growth rate of 20 mm/h. Growth direction contained a number of low-angle grain boundaries, which deteriorate their optical uniformity, whereas the crystals grown along the [110] direction had to low-angle grain boundaries. The necking process was also essential to enhance the optical quality. The formation of bubble inclusions was effectively suppressed by optimizing the combination of growth rates and crystal rotation rates.The absorption coefficient around 800 nm was large enough for pumping with a laser-diode of 808 nm which is conventionally used for Nd-lasers. Intensive emission was observed even above 1950 nm where the self-absorption could be neglected. The fluorescence decay time decreased from 2.1 to 0.5 ms with increasing Tm-concentration but is long enough for laser oscillation. Although the laser oscillation is under way, the Tm : GdVO_4 single crystals grown by the floating zone method are expected to be potential materials for 2 μm lasers.

激光雷达传感和医疗应用领域对人眼安全激光器的需求不断增加，掺铥 (Tm) 晶体是人眼安全激光器最有前途的材料之一，因为它们可以轻松地使用激光二极管进行泵浦。作为Tm激光器的主晶体，GdVO_4单晶从热导率和吸收系数的角度来看优于YAG和萤石等其他晶体。尝试了Tm掺杂的GdVO_4单晶并研究了其光谱性能。以纯氧流作为Tm掺杂高达20的生长气氛，通过浮区法成功生长了透明、无裂纹的Tm : GdVO_4单晶。 at％可以在20毫米/小时的高生长速率下进行，生长方向包含许多小角度晶界，这降低了它们的光学均匀性，而晶体沿着[110]生长。颈缩过程对于提高光学质量也至关重要，通过优化生长速率和晶体旋转速率的组合，可以有效抑制气泡夹杂物的形成。800 nm 附近的吸收系数足够大。对于通常用于 Nd 激光器的 808 nm 激光二极管的泵浦，甚至在 1950 nm 以上也观察到了强发射，其中自吸收可以忽略不计。随着Tm浓度的增加，时间从2.1毫秒增加到0.5毫秒，但对于激光振荡来说已经足够了。尽管激光振荡正在进行中，但通过浮区​​法生长的Tm：GdVO_4单晶有望成为2μm激光器的潜在材料。