Experimental Investigation of Thermal Lensing in End-pumped Nd:YVO4 Crystal Using a New Simple Approach

The stability of linear planar resonators involved in solid-state lasers is entirely decided by the thermal lens of the laser crystal. There exists a critical point between stable state and unstable state at which the thermally focusing point falls on the surface of one end mirror. Based on this fact, a new method for measuring the thermal focal length has been presented, and applied to three different Nd3+-doped (2%, 0.8%, and 0.5% ) Nd:YVO4 crystals at various absorbed pump power levels up to 10 W, the results show a good agreement with those of theoretical calculation. It also indicates that the thermal lensing is strongly dependent on the Nd3+-doped concentration, and is affected by crystal surface temperature, especially in the situation of weak thermal lensing.     

Thermal Lensing, Laser Performance at 1.06 μm and 0.53 μm of a NYAB Laser End pumped by a Diode laser array

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太阳光抽运固体激光工作物质的研究

探讨了适合太阳光抽运的固体激光器工作物质的选择方法,并分析了几种备选工作物质的性质。用Matlab对太阳光谱的现有数据进行了三次样条插值运算,建立了太阳光谱的局部精细离散化模型,并结合红宝石、Nd∶YAG、Yb∶YAG、Nd∶YVO4、Cr∶Nd∶GSGG、掺Nd3 的光学陶瓷和掺Yb3 的石英光纤等激光介质的吸收光谱,进行了太阳光谱与激光介质吸收谱的匹配分析。得出各激光介质所吸收的能量占太阳常量的百分比分别为24.51%,15.98%,2.35%,6.46%,43.91%,15.98%,7.63%。并在一定假设条件下,计算了各介质的阈值抽运功率体密度。综合以上激光介质的材料热特性,选取对太阳光吸收较多,阈值低且热特性好的Nd∶YAG,掺Nd3 光学陶瓷,Cr∶Nd∶GSGG为较适合的太阳光抽运激光工作物质。     

激光二极管端面纵向泵浦Nd:YVO_4激光器的热效应研究

针对激光二极管端面纵向泵浦Nd:YVO4激光器,本文理论和实验详细研究了Nd:YVO4晶体的热透镜效应。在激光二极管的中心波长分别为808nm和880nm及分别采用单端端面纵向泵浦和双端端面纵向泵浦结构情况下,实验测量了Nd:YVO4晶体的热透镜焦距,实验结果和理论预测基本吻合。同时在泵浦功率60W时获得了18.8W的连续基横模激光输出。     

端面泵浦双Nd: YVO4激光器中热效应对腔稳定性的影响

利用多个激光晶体串接方式可以提高固体激光器的输出功率. 发展双Nd: YVO₄晶体激光器, 将晶体的端面镀膜作为谐振腔的端面镜, 构成了平行平面谐振腔. 对平行平面谐振腔的等效腔进行了理论分析, 结果表明激光晶体吸收泵浦光产生的热透镜效应对保持腔的稳定性起到了重要的作用. 在国内首次进行了双端泵浦双Nd: YVO₄激光器的实验研究, 在抽运功率为 20.74 W时获得了11 W的1064 nm TEM00模激光输出, 其光-光转化效率约为53%. 并且对于不同掺杂浓度下的实验结果进行了讨论.     

Efficient diode-pumped Nd:YVO4 continuous-wave laser at 1.34 μm

We report a high-power continuous-wave(cw) diode-pumped efficient 1.34 μm Nd:YVO₄ laser. The laser properties of a low Nd³⁺-doped concentration of the Nd:YVO₄ crystal operating at 1.34 μm formed with a simple plane-concave cavity have been demonstrated. With the incident pump power of 22 W, an output power of 8.24 W was obtained, giving an optical conversion efficiency of 37.5% and slope efficiency of 40%. The thermal effects of cw end-pumped solid-state lasers were studied.     

Study on optical characteristics of Nd:YVO4/YVO4 composite crystal laser

Thermal effect in crystals is the main obstacle blocking diode-pumped solid state laser to get high and stable output power. Diffusion bonding crystal has been demonstrated to be an effective method to relieve the thermal lensing theoretically based on the numerical heat analysis to the end-pumped anisotropic laser crystal. The temperature distributions in Nd:YVO4/YVO4 composite crystal and conventional crystal were analyzed and compared. The end-pumped Nd:YVO4/YVO4 composite crystal laser was designed and set up with z-cavity. The maximum output powers of 9.87 W at 1064 nm and 6.14 W at 532 nm were obtained at the incident pump power of 16.5 W. The highest optical-optical conversion efficiencies were up to 59.8% at 1064 nm and 37.2% at 532 nm respectively.     

热透镜控制激光光束质量技术研究

在端面抽运固体激光器中,就如何改善在高抽运功率时输出激光的光束质量,提出一种激光器的设计方法。在激光器谐振腔中放入多根掺杂浓度不同的激光介质,利用激光介质内部产生的热透镜控制抽运光和基模振荡光的空间分布,并且最大限度地使抽运光的分布区和基模振荡光分布区重叠,实现抽运光与基模振荡光在空间上高度匹配,进而提高抽运光能量的利用效率和振荡光的光束质量。实验表明,在不同抽运功率下,抽运光和基模振荡光在晶体内部的光斑的空间分布可通过热透镜加以控制。在端面抽运功率200 W附近时,实现了抽运光与基模振荡光较高程度匹配,光束质量因子M2由14.7改善为4.1。     

固体激光器热透镜效应的调控

利用工作腔的热透镜模型, 分析了有激光发射下固体激光器的谐振腔配置对热透镜效应和稳定区的影响, 论述了通过改变谐振腔配置调控热效应的可行性.实验上, 使用一台Nd: YAG激光器对理论作了验证, 实现了对热透镜光焦度及稳定区分布的调控.     

端面抽运固体激光器热透镜效应的实验研究

提出一种易于实现、对激光器本身没有干扰、高空间精度、可实时测量介质热透镜的干涉测量方法. 并利用此方法全面研究了端面抽运Nd:YVO4激光器的热透镜效应，为认识激光介质的热效应和设计此类激光器提供了参考.  关键词： 热透镜 端面抽运 固体激光器     

Thermal Lensing, Laser Performance at 1.06 μm and 0.53 μm of a NYAB Laser End-pumped by a Diode-laser-array

The thermal lensing, output characteristics of an end-pumped NYAB laser with high pump power levels and operated at the fundamental wavelength, and the manner of self-frequency-doubling, have been investigated. The thermal lensing in the NYAB crystal was found to be significantly stronger than that in Nd:YVO4 crystal. A maximum output of 3.2 W at 1.06 μm was achieved with an optical conversion efficiency of 29.1％ and an average slope efficiency of 37.5％. These results were found to be slightly inferior to those of Nd:YVO4 crystal. When operated in the fashion of selffrequency-doubling, 23 mW green output was obtained at the incident pump power of 5 W, such inefficient operation was attributed to the large mode size in the NYAB crystal.     

高稳定LD端面泵浦腔内倍频Nd∶YVO4/LBO连续红光激光器

设计出一种能够较好地补偿激光晶体热效应的激光谐振腔,实现了高稳定LD单端泵浦LBO腔内倍频Nd∶YVO4连续红光激光器.当晶体吸收的泵浦功率为24.56 W时,671 nm激光功率达到1.203 W,光-光转换效率4.9%,激光模式为TEM00模.在输出功率为1.08 W时,激光器1 h功率不稳定度为0.52%.     

第三类热边界条件对激光晶体热效应的影响

以各向异性半解析热分析理论为基础,研究矩形横截面Nd∶YVO4激光晶体在有第三类热边界条件工作时,激光晶体温度场分布和晶体抽运面热形变分布.通过激光晶体工作特点分析,建立符合激光晶体工作状态的热模型.利用各向异性介质热传导方程的半解析求解方法,得出了矩形截面Nd∶YVO4晶体的温度场、端面热形变场的通解表达式.研究结果表明：当使用输出功率为15 W半导体激光器端面中心入射Nd∶YVO4晶体（晶体掺钕离子质量分数为0.5%）时,在抽运端面中心获得499.5 K最高温度和0.99 μm最大热形变量.和将第三类热边界条件近似为第二类热边界条件的通用做法相比更准确.这种方法可以应用到其它激光晶体热问题研究中,为有效解决激光系统热问题提供了理论依据.     

溶胶-凝胶法制备SiO2基片Er3+∶Al2O3光学薄膜

用溶胶凝胶法在SiO2 基片上提拉制备了掺Er3 + ∶Al2 O3 光学薄膜。采用扫描电子显微镜、原子力显微镜、差热热重分析仪、X射线衍射仪研究了掺Er3 + ∶Al2 O3 光学薄膜的形貌和结构特性。在 90 0℃烧结后 ,SiO2 基片上提拉 15次形成厚度 8μm掺摩尔比 0 .0 1Er3 + 的面心立方结构γ Al2 O3 薄膜具有明显 (110 )择优取向 ,掺摩尔比 0 .0 1Er3 + 对γ Al2 O3 的晶体结构和结晶生长过程未产生显著影响。薄膜具有均匀多孔结构 ,平均粒径为 30～ 10 0nm ,平均孔径为 5 0～ 10 0nm ,表面起伏度为 10～ 2 0nm。掺摩尔比 0 .0 1Er3 + ∶γ Al2 O3 薄膜 ,获得了中心波长为1.5 34μm(半峰全宽为 36nm)的光致发光谱。     

第三类热边界条件对激光晶体热效应的影响

以各向异性半解析热分析理论为基础,研究矩形横截面Nd:YVO4激光晶体在有第三类热边界条件工作时,激光晶体温度场分布和晶体抽运面热形变分布.通过激光晶体工作特点分析,建立符合激光晶体工作状态的热模型.利用各向异性介质热传导方程的半解析求解方法,得出了矩形截面Nd:YVO4晶体的温度场、端面热形变场的通解表达式.研究结果表明:当使用输出功率为15 W半导体激光器端面中心入射Nd:YVO4晶体(晶体掺钕离子质量分数为0.5%)时,在抽运端面中心获得499.5 K最高温度和0.99 μm最大热形变量.和将第三类热边界条件近似为第二类热边界条件的通用做法相比更准确.这种方法可以应用到其它激光晶体热问题研究中,为有效解决激光系统热问题提供了理论依据.     

高稳定LD泵浦腔内倍频Nd∶YVO4/KTP连续绿光激光器

设计出一种能够较好地补偿激光晶体热效应的激光谐振腔，实现了高稳定LD单端泵浦KTP腔内倍频Nd∶YVO₄连续绿光激光器.当晶体吸收的泵浦功率为24.56 W时，532 nm激光功率达到5.3 W，光-光转换效率达到21.6％，激光模式为TEM00模.在输出功率5W左右时，激光器1 h功率不稳定度优于0.6％     

全固态高功率连续单横模Nd:YVO4/LBO绿光激光器

报道了激光二极管泵浦的高功率连续单横模绿光激光器。考虑到激光晶体因吸收泵浦光而产生的热透镜效应,我们选择低掺杂浓度Nd:YVO4激光晶体,设计了V字型热不灵敏折叠式驻波谐振腔,利用I类非临界相位匹配LBO非线性晶体,当泵浦功率为23 W时,得到7 W单横模532 nm绿光输出功率,光-光转化效率为33%,长期功率稳定性优于1.6%(自由运转3小时)。     

LD端面泵浦不同掺杂离子YAG晶体的热效应研究

通过建立激光晶体热传导模型,针对相同基质YAG晶体不同掺杂离子,求解泊松方程,得到不同Nd3+和Yb3+掺杂浓度的YAG晶体内温度场分布,并进行了对比分析。研究结果表明:在相同条件下,随着Nd3+和Yb3+掺杂浓度的增加,YAG晶体端面中心温度升高,晶体中心轴温度衰减越快,热焦距越小;当Yb3+掺杂浓度达到Nd3+掺杂浓度的近10倍时,热效应基本相同。这一结论为降低同基质晶体的热效应提供了理论依据。     

6.2 W diode-end-pumped 1313 nm Nd:YLF laser

We presented a compact and efficient diode-end-pumped 1313 nm Nd:YLF laser with an effective pump system and no additional insertion loss. The different thermal lensing effects along the ?? and ?? polarizations in an a-cut Nd:YLF crystal were investigated. 6.2 W output power of the polarized 1313 nm laser was obtained at the absorbed pump power of 17.5 W, corresponding to the optical-optical efficiency of 35% and the slope efficiency of 41%.     

20-Hz operation of an eye-safe cascade Raman laser with a Ba(NO3)2 crystal

Operation of a 1.598-μm eye-safe third-Stokes Raman laser with a Ba(NO₃)₂ crystal pumped by a 1.064-μm Nd:YAG laser is described. We observed a substantial decrease in the output energy during the first 50 s of the continuous operation at 20 Hz. The energy drop is ∼76% of the initial third-Stokes output. We confirmed negative thermal lensing and thermally induced birefringence in the crystal. With a concave cavity mirror at a matched curvature to the thermal lensing, we obtained an output energy of 11 mJ at 20 Hz. TEM₀₀ output was also obtained with a smaller pump-beam diameter with a highest conversion efficiency of 15.5% for a pumping power of only 45 MW/cm² (0.9 J/cm²). Received: 20 November 2001 / Revised version: 20 February 2002 / Published online: 2 May 2002