【作者】 兰瑞君；

【导师】 任诠； 侯学元； 王正平；

【作者基本信息】 山东大学 ， 光学工程， 2010， 博士

【摘要】 自激光器诞生以来,人们一直没有停止探索新激光介质材料的脚步。按照所用的激光介质种类分,激光器可分为气体激光器、染料激光器、半导体激光器和固体激光器。其中固体激光器由于体积小、效率高、输出稳定、泵浦灵活等优点,在国防、科技、医疗等各个领域都有广泛应用。一直以来,单晶是固体激光器中应用最广泛的激活介质,其类型的多样化决定了激光器的多样化,大大增加了激光器的设计灵活性。目前在高功率固体激光器中,Nd：YAG晶体由于其良好的热学、光学等综合性能,成为最成熟和应用最广泛的激光介质,但它也存在发展瓶颈,比如掺杂浓度低、生长成本高等；在中小功率固体激光器中,Nd：YVO4晶体由于具有较大的吸收和发射截面而得到普遍应用,但热效应明显以及光损伤阈值较低的缺陷影响了其在高功率激光器中的应用。近年来,以透明陶瓷作为激光介质的固体激光器引起了人们越来越多的关注。透明陶瓷作为一种新兴材料,具有高热导率、低电导率、高硬度、耐磨损、耐腐蚀等一系列优异的综合性能。与玻璃相比,陶瓷具有更好的韧性和抗光伤能力；与单晶相比,陶瓷具有更短的生产周期、更高的掺杂浓度和更低的生产成本。衡量透明陶瓷质量的参数主要有：散射率、气孔体积、晶粒尺寸和晶界宽度等。随着陶瓷制备工艺的日趋精湛,上述各参数得到了不断改进,出现了一系列优秀的透明陶瓷材料,例如：Nd：YAG陶瓷、Yb：YAG陶瓷、Yb：Y2O3陶瓷和Nd：Lu2O3陶瓷等。其中Nd：YAG陶瓷已经实现了部分产业化并且在光谱性能、荧光寿命等方面达到了与Nd：YAG单晶一致的程度,再加上易于生长成大尺寸、允许做成高掺杂浓度等特点弥补了Nd：YAG单晶所存在的缺陷,为固体激光器的发展带来了更加广阔的前景。本文系统研究了以Nd：YAG透明陶瓷作为激光介质的全固态激光器的连续、脉冲以及双波长的输出性能,并与某些单晶的实验结果进行了比较,其主要研究内容包括：1)对LD泵浦的Nd：YAG陶瓷1.06μm、1.3 pm和946 nm连续激光器进行了研究。1.06μm连续激光实验中,当泵浦功率为21.6 W时,获得了11.3 W的连续激光输出,相应的光-光转换效率和斜效率分别为52.3%和54.4%。在高泵浦功率下并未出现饱和现象,因此继续加大泵浦功率有望获得更高输出。1338 nm连续激光实验中,当泵浦功率为20.5 W时,获得了1.05 W的连续激光输出,相应的光-光转换效率为5.1%。由于在1.3μm波段存在1319 nm和1338 nm的模式竞争,为了得到单一的1338 nm波长激光输出,在腔内加入了损耗片以抑制1319nm波长激光,因此转换效率较低。946 nm连续激光实验中,分别采用了三块不同长度的陶瓷样品,通过理论计算和实验验证得出了陶瓷的最佳长度。利用长度为5 mm的陶瓷样品,当吸收泵浦功率为10.5 W时,获得了1.46 W的连续激光输出,相应的光-光转换效率和斜效率分别为13.9%和17.9%。2)利用KTP和BiBO作为倍频晶体,对LD泵浦的Nd：YAG陶瓷连续倍频绿光激光器进行了研究。实验中发现,KTP晶体的倍频性能要优于BiBO晶体,当利用KTP晶体进行倍频时,泵浦功率为26.4 W时,绿光输出功率为1.86 W,光-光转换效率为7%。在输出功率为1 W时用针孔法对绿光光斑的一维空间分布进行了测量,结果显示符合高斯分布,经计算光束传输因子M2约为1.7。这是国内首次利用Nd：YAG陶瓷进行的LD端面泵浦高功率连续波绿光输出。3)对LD泵浦的Nd：YAG陶瓷1.06μm被动调Q脉冲激光器进行了研究。1.06μm脉冲激光实验中,分别用到了Cr：YAG和GaAs两种饱和吸收体。Nd：YAG陶瓷／Cr：YAG被动调Q实验采用了三块不同初始透过率的饱和吸收体,所得到的最大脉冲能量、最短脉冲宽度和最高峰值功率分别为：188μJ、3.16 ns和59.5 kW。Nd：YAG陶瓷／GaAs被动调Q实验所得到的最短脉冲宽度、最大单脉冲能量以及最高峰值功率分别为为17 ns、41.6μJ和2.44 kW。通过与Nd：LuVO4晶体、Yb：NaY(WO4)2晶体被动调Q实验结果的比较,突显了Nd：YAG陶瓷在高功率激光器应用中的优势。4)对LD泵浦的Nd：YAG陶瓷三种不同的双波长激光器进行了研究。首次实现了Nd：YAG陶瓷1052 nm连续激光输出,最大输出功率为6.19 W,相应的光-光转换效率和斜效率分别为35.8%和39%。以Cr4+：YAG作为饱和吸收体和调制选频器件,实现了1064 nm和1052 nm双波长脉冲激光输出,并从理论上解释了两种波长的产生原因和顺序,其中最短脉冲宽度、最大脉冲能量和最高峰值功率分别为：4.8 ns、103.2μJ和21.5 kW。实现了1319 nm和1338 nm双波长连续和脉冲激光输出,并测量了总输出功率中1319 nm和1338 nm激光所占比例,最大连续输出功率为5.92 W,最大脉冲输出功率为226 mW,最短脉冲宽度和最高重复频率分别为15 ns和133 kHz。利用激光介质的高增益特性,直接将其未镀膜的抛光端面作为输出耦合镜,实现了Nd：YAG陶瓷、Nd：YAG晶体、Nd：YVO4晶体免镀输出镜介质膜的1064 nm连续激光。其中利用陶瓷得到的最大输出功率达到1.74W,光-光转换效率和斜效率分别为13.0%和19.3%,优于相同实验条件下Nd：YAG晶体和Nd：YVO4晶体的结果。在此基础上实现了1064 nm、1319 nm、1338 nm多波长连续激光运转,最大输出功率为3.2 W。通过以上研究,证明了Nd：YAG陶瓷作为激光工作物质的优越性,预示了它在多种固体激光装置中具有重要应用前景。更多还原

【Abstract】 To make laser device more and more efficient, people never stop searching for new laser gain material ever since the day when laser was invented. According to different laser materials, there are four series of lasers, gaseous state laser, dye laser, semi-conductor laser and solid state laser. Due to the compactness, high efficiency, stable output and various pump modes, all-solid-state lasers have wide applications in national defense, scientific research and medical treatment. Single crystals are the most popular laser gain material,the variety of the single crystal allows various laser design proposals. Due to the good thermal and optical characteristics, Nd:YAG crystal has been considered to be an exellent laser gain medium in high power solid-state lasers, but it has its own defects, such as low doping level and high cost. Nd:YVO4 crystal has large absorption and emission cross-sections, it is favorable in middle-power and pulsed laser operation, but the serious thermal effect and low damage threshold show its limit in high-power laser applications.In recent years, people became more and more interested in ceramic lasers. As a newly developed laser material,transparent ceramics have a series of good characteristics, such as high thermal conductivity, low electrical conductivity, high hardness et al. Compared with glass, ceramic has better toughness and higher damage threshold. Compared with single crystal,ceramic has shorter growing period and higher doping level.With the development of the sintering technology, many excellent ceramic gain materials have been obtained, such as Nd:YAG ceramic, Yb:YAG ceramic, Yb:Y2O3 ceramic, Nd:Lu2O3 ceramic et al.Compared with Nd:YAG crystal, Nd:YAG ceramic has comparable optical and even better physicochemical characteristics. Meanwhile, ease of fabrication and high doping level make ceramic more useful in many fields.In this paper, we focused our research on the continuous wave (CW), pulsed and dual-wavelength Nd:YAG ceramic lasers, the main contents of this thesis are as following,1)LD-pumped CW 1064 nm,1338 nm and 946 nm Nd:YAG ceramic lasers were demonstrated. In the 1064 nm regime, we obtained 11.3 W CW output power at an incident pump power of 21.6 W, corresponding to an optical conversion efficiency of 52.3%, the slope efficiency was 54.4%. Under high pump power, no saturation was observed, which indicated higher power scaling can be expected. In the 1338 nm regime, we obtained 1.05 W CW output power at an incident pump power of 20.5 W, corresponding to an optical conversion efficiency of 5.1%. In the 946 nm regime, three different samples were used. With the 5 mm long Nd:YAG ceramic, we obtained 1.46 W CW output power at an incident pump power of 10.5 W, corresponding to an optical conversion efficiency of 13.9%, the slope efficiency was 17.9%.2) LD pumped Nd:YAG ceramic/KTP and Nd:YAG ceramic/BiBO green lasers were demonstrated. Through the experiment we found that the KTP crystal was superior to the BiBO crystal in frequency doubling. When the type-Ⅱcut KTP crystal was used as a frequency doubler, the maximum 532 nm green output was 1.86 W, and the optical conversion efficiency was 7%. The distribution of the green laser facula was found to be Gaussian type and the M2 factor was measured to be 1.7. To the best of our knowledge, this is the first report of a LD-end pumped high power Nd:YAG ceramic green laser.3) LD pumped Nd:YAG ceramic/Cr:YAG and Nd:YAG ceramic/GaAs passively Q-switched lasers were demonstrated. When the Cr:YAG crystal was used as saturable absorber, the largest pulse energy, shortest pulse width and highest peak power were measured to be 188μJ、3.16 ns and 59.5 kW, respectively. When the GaAs crystal was used as saturable absorber, the largest pulse energy, shortest pulse width and highest peak power were measured to be 41.6μJ、17 ns and 2.44 kW, respectively. Compared with the passively Q-switched results of Nd:LuVO4 and Yb:NaY(WO4)2 crystals, Nd:YAG ceramic has better performance.4) Three different kinds of dual-wavelength Nd:YAG ceramic lasers were studied. CW 1052 nm laser was obtained with Nd:YAG ceramic for the first time. The maximum output power was 6.19 W, corresponding to an optical conversion efficiency of 35.8% and slope efficiency of 39%. Using Cr:YAG as saturable absorber and frequency selector, we realized 1052 nm and 1064 nm dual-wavelength laser output, the largest pulse energy, shortest pulse width and highest peak power were measured to be 103.2μJ、4.8 ns and 21.5 kW, respectively. We realized 1319 nm and 1338 nm CW and pulsed dual-wavelength laser output. For both CW and pulsed output, we measured the ratio of 1319 nm and 1338 nm lasers. The maximum CW output power was 5.92 W and the pulsed part was 226 mW, the shortest pulse width and highest repetition rate were 15 ns and 133 kHz. Due to the high gain coefficient of laser materials, we realized 1064 nm Nd:YAG ceramic, Nd:YAG crystal and Nd:YVO4 crystal CW output laser without extra output coupler. The maximum output power was 1.74 W with Nd:YAG ceramic, corresponding to an optical conversion efficiency of 13.0%, the slope efficiency was 19.3%. Based on this idea, we realized 1064 nm,1319 nm and 1338 nm multi-wavelength laser output, the maximum output power was 3.2 W.With all the studies above, Nd:YAG ceramic has been proved to be an excellent laser gain material, which can find applications in variety of lasers.更多还原