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.

在激光雷达敏感性和医疗应用领域，对眼部安全激光的需求一直在增加。 Thulium（TM）掺杂的晶体是眼部安全激光器的承诺材料之一，因为可以使用激光二极管轻松泵送它们。作为TM激光剂的宿主晶体，GDVO_4单晶从热导率和滥用系数的角度优于其他晶体，例如YAG和氟矿。在这项研究中，尝试了TM掺杂的GDVO_4单晶的浮动区生长并研究了光谱特性。透明的无裂纹TM：GDVO_4单晶通过浮动区方法成功生长，使用纯氧气流动作为生长大气。以20 mm/h的高生长速率，最多可达到20％的TM掺杂。生长方向包含许多低角度晶界，这些晶界决定了它们的光均匀性，而沿[110]方向生长的晶体必须以低角度的晶界。颈部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，有效地抑制了气泡夹杂物的形成。在800 nm左右的吸收核心足够大，足以用808 nm的激光二极管泵送，该激光二极管通常用于ND激光剂。即使在1950 nm以上，也可以忽略自我吸收。随着TM浓度的增加，荧光衰减时间从2.1下降到0.5 ms，但足够长的时间用于激光振荡。尽管正在进行激光振荡，但通过浮动区方法生长的TM：GDVO_4单晶有望是2μM激光器的潜在材料。