【作者】 李晓敏；

【导师】 卓壮；

【作者基本信息】 山东师范大学 ， 光学， 2007， 硕士

【摘要】 激光二极管(LD)泵浦的全固态激光器以高效率、结构紧凑、工作稳定、寿命长和全固化等特点,在材料加工、军事、医疗、科研等方面获得了日益广泛的应用,目前已成为国际上新型固体激光器的研究和发展热点。但是由于激光工作物质吸收泵浦能量而在激光晶体内产生一定的温度梯度,并且由于端面形变和热效应引起的激光晶体折射率的变化导致热透镜效应,影响了激光光束的质量,给激光器的设计带来了困难。为改善高功率激光器激光工作物质的热效应,本文采用先光胶后热处理的键合工艺,研制了Nd:YVO4/ YVO4复合晶体,测试了复合晶体的激光特性,并与相同掺杂浓度和体积的单一晶体进行了比较,发现热键合晶体由于键合面处有效地热传导,明显的改善了热键合晶体的热透镜效应;分析了复合晶体内的温度场分布,与单一晶体进行了对比,进一步证明了复合晶体具有良好的导热特性。另一方面,波长1570nm的人眼安全激光,在激光测距上有广泛的应用,全固态的光学参量振荡激光器(Optical Parametric Oscillator,简称OPO)是实现1570nm人眼安全激光的主要技术途径, KTA-OPO系统更是其中的研究热点之一。本论文主要对LD端面泵浦的Nd:YVO4/ YVO4复合晶体激光器以及调Q运转的Nd:YAG/KTA内腔式单共振光参量振荡激光器进行了理论分析和实验研究。论文主要内容概括为:1、回顾了全固态激光器的历史和发展;介绍了复合晶体的发展历史与研究现状;总结了腔内倍频激光器和1570nm人眼安全激光器的研究现状。2、介绍了Nd:YVO4/ YVO4复合晶体的制备方法,比较分析了Nd:YVO4单一晶体与Nd:YVO4/ YVO4复合晶体的基频激光特性。实验证明复合晶体能够有效地降低晶体内的温度梯度,减小由端面变形带来的热透镜效应,在获得高功率固体激光器方面有很大的应用前景。目前我国对光学晶体的热键合还处于起步阶段,加快它的研究和发展,对促进我国激光事业的发展有着十分重要的作用。3、分析了倍频激光器的连续运转理论和KTP晶体相位匹配理论,从理论及实验上研究了连续运转的LD端面泵浦Nd:YVO4/ YVO4复合晶体KTP倍频绿光激光器,采用V/Z两种腔型,光-光转换效率分别达到31.3%和37%。4、简单介绍了Cr4+:YAG、GaAs被动调Q理论,首次采用Nd:YVO4/YVO4复合晶体实现了调Q激光输出,发现在相同泵浦功率下,相比单一晶体,复合晶体调Q激光输出的脉宽更窄,重复频率、单脉冲能量和峰值功率更高,脉冲对称性更好;在平面波近似下,根据速率方程理论模拟了调Q脉冲的输出特性,发现实验值和理论值相符合。5、在LDA侧面泵浦的Nd:YAG激光器的谐振腔中置入非临界相位匹配的KTA晶体,构成内腔式光学参量振荡器(IOPO),采用平凹短腔结构,有效降低了阈值,实现了1570nm准连续激光振荡输出。测量了不同声光重复频率和不同输出透过率下1570nm激光输出的各项特性参数以及对泵浦阈值和输出脉冲波形的影响,并对实验中出现的饱和现象作了解释。当泵浦电流14.5A,声光重复频率4KHZ,输出透过率30%时,在保持单脉冲输出情况下,KTA-OPO获得1570nm平均输出出功率563.3mW,峰值功率达到5. 6×104W。本论文的主要创新点:1.传统的键合工艺使用高温高压的方法,导致热键合面出现粒子的渗透,本文通过深度光胶的方法,即通过键合面处的精确抛光,实现两个相同晶向的晶体的光胶,然后通过合适的热处理,实现热键合面处分子键的重排和渗透,从而达到稳定键合的目的。2.以Nd:YVO4/ YVO4复合晶体作为激光工作物质,首次系统的研究了复合晶体的基频、倍频及调Q输出特性。由于热键合技术对工艺水平的要求较高,研究难度较大,我国对光学晶体热键合技术的研究还非常少,目前只有一些尝试性的研究,关于复合晶体激光特性的相关研究更少。3.首次利用LD阵列侧泵声光调Q的Nd:YAG激光器作泵源,研究了内腔式更多还原

【Abstract】 Diode-pumped solid-state laser is widely used in material processing, military, medical therapeutics, basic research, etc for their advantages, such as high efficiency, compactness, stability, long lifetime and all solid-state construction, now it has become the researching emphasis because unique merits. In the research area of laser diode end-pumped all-solid state lasers,a temperature gradient is formed in the laser crystal because of the absorption of the pump power. Because the temperature at the center of the laser crystal is higher comparing with the edge, a deformation of the surface appeared and a thin convex is formed. In addition, the change of refractive index of the laser crystal can also devote to the thermal lens effect and make the designing of the laser cavity more difficult.We developed the composite crystal of Nd:YVO4/ YVO4 using the diffusion bonding method, tested its basic optical property,and finded that the composite crystal has much longer thermal focus length under the same pump condition comparing with the single crystal.The laser with output wavelength at 1570nm is widely used in range finding because they are relatively safe to people’s eyes. Optical Parametric Oscillator (OPO) pumped by 1064nm Nd:YAG laser at 1570nm is one of the most effective way to get the eye-safe laser.A LD pumped Nd:YVO4/ YVO4 composite crystal laser and a acousto-optically (AO)Q-Switched Nd:YAG intracavity optical parametric oscillator(OPO) are researched theoretically and experimentally.The content of this dissertation is listed as below:1. The history and development of all solid state lasers and Nd:YVO4/ YVO4 composite crystal are reviewed; the research statue of frequency-doubling laser and 1570nm wavelength eye-safe laser are summarized.2. The developing method of Nd:YVO4/ YVO4 composite crystal is introduced, the optical properties of Nd:YVO4/YVO4 composite crystal and Nd:YVO4 single crystal are studied contrastedly . It is demonstrated that the composite crystal can effectively recede the temperature of crystal, relieve the thermal lens and get higher output power. 3. The frequency-doubling property of Nd:YVO4/YVO4 composite crystal with KTP is studied in a“V/Z-shaped”folded cavity, giving an optical conversion efficiency of 31.3% and 37%.4. The characters of Cr4+:YAG and GaAs crystal on Q-switching are introducing, get the Q-switching laser output using Nd:YVO4/YVO4 composite crystal for the first time,and find that comparing with the single crystal , the refraction loss caused by the thermal effect is little ,the thermal lens effect is improved, the laser efficiency of the composite crystal is much higher.5. 1570nm quasi-continuous laser is realized by putting non-critical-phase-matched KTA into LDA side-pumped Nd:YAG AO Q-switched laser which constructed an intra-cavity OPO; The output power of 563.3mW at 1570nm is produced with the frequency of 4kHz at the incident current of 14.5A, the output coupler transmission is 30%, and the peak power achieves 5. 6×104W.The innovative points:1. Comparing with the former diffusion bonding method, which use high pressure and high temperature in the diffusion bonding process, in this paper, a deep optical contacting method is used. In this process, the diffusion bonding surface is precisely polished and contacted by the intra-molecular strength ( H-bond), and then it was put in an even temperature field and was heat treated by a suitable temperature. In the process of heat treatment, the molecular bond is rearranged and a steady and strong bond is formed.2.The optical properties of Nd:YVO4/YVO4 composite crystal were systemicly studied for the first time Because the research work of the technique of thermal bonding is difficult, there is little study on the technique of thermal bonding in our country.3. The output properties of 1570nm laser were researched for the first time by putting a non-critical-phase-matched KTA into LDA side-pumped Nd:YAG AO Q-switched laser to construct an intra-cavity OPO.更多还原