基于Er:YAP晶体上转换机制的可见及紫外连续激光器研究

This project, choosing the Er:YAlO3（Er:YAP）crystals with the lower symmetry configuration as the materials of upconversion laser, studies tunable upconverstion lasers, at the imperative lasers with output wavelength approximate visble band of 550nm and approximate ultraviolet band of 320nm in medical treatment field studied in foundation and application. In this process, the merits of the crystal, whose large stimulated emision cross section and long fluorescent lifetime, and whose chemical, thermal and Mechanical properties, particularly relevant to laser diode pumping, are fully used. In respect of the foundation, this project studies the energy level radiant property and upconversion mechanisms of materials; estimates the upconversion laser performance of Er:YAP crystal; and illustrates upconversion radiant transitions mechanisms of 550nm and 320nm laser transitions after Er3+ ions excitated by two steps. In respect of the experiments, this project chooses a 980-nm centre wavelength of laser diode to pump the crystal of Er:YAP, to realize an upconversion continuous laser of 550nm, and then investigates the output property of laser ; this project also adopts laser sources of 532nm to pump the crystal of Er:YAP, and then investigates the amplification phenomenon of ultraviolet laser or continuous output property of ultraviolet laser.

本项目选用低对称结构的Er:YAlO3（Er:YAP）晶体作为上转换激光的工作物质。充分利用该晶体化学、热和机械特性，以及受激发射截面大、荧光寿命长且适合二极管激光器泵浦等优点，在基础和应用两个方面对医疗急需的可见光波段550nm和紫外波段320nm附近可调谐上转换连续激光进行研究。 在基础方面，对工作物质的能级辐射性质和上转换发光机理进行研究，评价Er:YAP晶体的上转换激光性能，阐明Er3+通过二步激发后实现550nm和320nm激光跃迁的上转换辐射跃迁机理。在应用方面，采用中心波长为980nm的二极管激光器泵浦Er:YAP晶体实现550nm上转换激光连续输出，并对此激光的输出特性进行研究；选用532nm的光源激励Er:YAP晶体，研究其紫外激光放大现象及连续输出特性。

本项目是基于Er:YAP晶体连续波上转换激光的优异性能，对治疗皮肤病急需320nm激光光源和治疗青光眼急需550nm激光光源展开研究。. 通过对Er:YAP晶体能级辐射性质及上转换发光机理的研究，明确了550nm和320nm激光光源的上转换发光机理和能级辐射性质。确定了实现550nm激光光源的最佳泵浦波长分别为980nm/800nm，明确 2H11/2和2S3/2组成的耦合能级，Er3+粒子从耦合能级跃迁到4H15/2 能级，可实现550nm激光输出，即2H11/2→4H15/2或2S3/2→4H15/2；确定了实现320nm激光光源最佳泵浦波长为532nm，Er3+粒子从2P3/2能级越迁到基态4H15/2能级，产生320的激光输出，即2P3/2→4H15/2。. 通过对Er:YAP 晶体550nm上转换连续可调谐激光性能的研究，实现了激光放大现象，获得了不同轴向的荧光功率谱，计算出了Er:YAP晶体在550nm附近的吸收截面、发射截面和增益截面，具体的数据为：550nm附近的截面峰值在543nm，吸收截面为1.83×10-21cm2，受激发射截面为1.23×10-21cm2；以ß=0.8为例，增益截面在538-562nm之间为正值，有宽且较为平缓的发射峰，在543、547和550nm附近增益系数较大，分别为0.619×10-21cm2、0.328×10-21cm2和0.158×10-21cm2，说明Er:YAP晶体在550nm附近具有宽调谐特性。在实验上设计并尝试了多种550nm上转换激光器结构，计算出激光器振荡光斑直径小于30μm，激光晶体的单位面积大约需要3.8×105W/cm2的能量密度为激光器的泵浦阈值。. 通过对Er:YAP 晶体320nm上转换连续可调谐激光放大（输出）性能的研究，获得该波段荧光功率谱，证实该波段激光放大现象。