热离子交换型铝锗酸盐波导玻璃中钬离子的1.2μm近红外荧光发射

1. 2 μm Near Infrared Fluorescence Emission of Holmium Ions in Thermal Ion-exchanged Aluminum Germanate Waveguide Glasses

采用高温熔融法制备了适用于钾钠离子交换波导的钬离子掺杂铝锗酸盐玻璃,并对热离子交换玻璃样品的波导折射率分布和红外光谱特性进行了表征。实验结果表明,在390℃的KNO_3熔盐中热离子交换4 h时,波导玻璃折射率最大改变量为0.006 9,K^+-Na^+热离子交换有效扩散深度为7.802μm,有效扩散系数达0.063μm^2/min。K^+-Na^+离子交换有效扩散系数比磷酸盐玻璃低,与MP19硅酸盐玻璃相当,但明显高于BK7玻璃和硼硅酸盐玻璃,其热离子交换过程易于控制。在644 nm泵浦光下可观察到Ho^(3+)归属于~5I_6→~5I_8的1.196μm近红外有效发射,最大受激发射截面为2.30×10^(#21)cm^2。当Ho^(3+)在~5I_6能级的分数因子超过0.6时,增益截面达10^(#21)cm^2量级以上。有效的近红外荧光发射和稳定的波导性能表明钬掺杂铝锗酸盐玻璃是~1.2μm波导激光器潜在的增益介质。

Ho^3+doped aluminum germanate glasses adapting for K^+-Na^+ion-exchanged waveguide were fabricated by high temperature melting technique.The thermal ion-exchanged waveguide refractive index profile and infrared spectral characteristic of the glasses were measured.These experimental results reveal that the maximum change of refractive index in waveguide glasses is 0.006 9 when Ho^3+doped aluminum germanate glasses are immersed in KNO3 molten salt at 390℃for 4 h.Effective diffusion depth and coefficient of K+-Na+thermal ion exchange are 7.802μFm and 0.063μm^2/min,respectively.K^+-Na^+effective diffusion coefficient in aluminum germanate glass is lower than that in phosphate glass and approximately equals to that in MP19 silicate glass,but significantly higher than those in the BK7 glass and borosilicate glass,which indicates the thermal ion-exchanged process can be controlled easily.Effective 1.2μm near infrared emission belonging to 5I 6→5I 8 transition could be observed under 644 nm pump whose the maximum stimulated emission cross-section at 1.196μm is derived to be 2.30×10^-21 cm^2.For the 5I 6→5I 8 transition of Ho^3+,the gain cross-section achieves a magnitude of 10^-21 cm^2 when fraction factor P exceeds 0.6.Effective near-infrared fluorescence and perfect waveguide performance demonstrate that Ho^3+doped aluminum germanate glass is a kind of potential gain medium in^1.2μm waveguide laser device.