采用一台输出波长为1064 nm的NdYAG调Q激光器，以不同辐照方式对光学元件表面污染物引起的损伤开展了系统的实验研究。在确定了K9 玻璃和熔石英元件基板零几率损伤阈值的基础上，针对金属粒子污染物和有机污染物分别进行了元件损伤特性实验研究，分析了表面污染物造成元件损伤阈值下降的诱导机理。

实验发现光学材料的损伤与激光波长、材料特性、激光脉宽等因素有关，而且光学材料损伤的最终态是不一样的，这个态可以是熔化、碎裂或蒸发。为了解释这些现象，从材料的热传导方程出发半定量地讨论了光学材料损伤机理，指出了一个关键参数决定了激光诱发损伤与激光脉宽τp的关系，它就是光学材料内的夹杂物把热量传递给光学材料体所需时间τ。在τpτ时，损伤阈值由激光辐射强度决定；在τpτ时，损伤阈值由激光辐射能量密度决定。

Gain medium of modern high-average-power solid-state lasers can produce distortion for the reason of thermal effect, such as YAG. Wavefront distortion and depolarization often occur simutaneously. The thermal stress of the high-power solid state laser slab is becoming a serious problem for hindering the further power increasing of the laser. A method for calculating the thermally induced refraction index in a pumped heat capacity slab laser was studied. In this method, the fourth-rank piezo-optics tensors of YAG crystal were transformed from the crystal lattice coordinate system to the laboratory coordinate system. With these new tensors, the thermally induced stress birefringence in a solid-state laser can be analyzed easily for any stress distribution. Furthermore, the calculations show that the birefringence in a zigzag slab depends on the angle under which the slab is cut from the boule. A theoretical description of the thermal and stress characteristics of heat capacity slab laser in two dimensional was also presented.

高平均功率固体激光器的增益介质由于受热而容易发生畸变,如常用材料YAG,波前畸变和去偏振现象会同时发生,高热负载固体激光介质的热效应已成为制约激光器输出功率进一步提高的严重障碍。给出一种计算热容型板条激光器热感生折射率的方法。把YAG晶体的四阶压光张量从晶胞坐标系转换到实验室坐标系,采用经过坐标转换后的新的张量,可以分析在YAG激光器中任意应力分布引起的热感应双折射。进一步的计算表明,在zigzag板条激光器中,应力双折射率与板条从晶体毛胚上切割成材的角度有关。同时也对热容板条激光器的热效应和应力特性进行了二维的理论性概述。

The solid state heat capacity laser (SSHCL), as one of the most important high-power solid-state lasers, has attracted extensive attention. Numerical simulation of temperature and stress distributions of laser crystal slab in the heat capacity operation mode is a major means to understand the specific property of the laser. Using the method of plane stress approximation, the two-dimensional (2D) mathematical formulas that describe the temperature and stress distributions of laser diode (LD) pumped heat capacity slab laser are derived. Then the absorbed pump power density, 2D distributions of temperature and index of refraction are also analyzed and discussed. According to the results, the 2D distributions of temperature and stress are more homogeneous than that of the one-dimensional distributions.

Based on the laser rate equations in a typical four-level system, we research the temperature-dependent gain characteristics of a solid-state heat-capacity laser (SSHCL) involving the small-signal gain coefficient and the gain distribution's uniformity. The influences of doping concentration of active ions and initial operating temperature on the small-signal gain coefficient are discussed for Nd-doped glass heat-capacity laser. Furthermore, the gain distributions of a slab laser gain medium operating in SSHCL mode are discussed.

固体热容激光器(SSHCL)作为高功率固体激光器的一个重要发展方向, 引起人们广泛关注。数值模拟激光介质板条在热容方式下工作的温度和应力分布是了解该类激光器工作特性的一种有效手段,采用平面应力近似法导出了半导体激光器抽运热容激光介质板的二维温度和应力分布公式,同时也对二维抽运光吸收密度、介质板温度分布和折射率变化进行了分析与讨论。数值计算的结果表明二维效应的温度分布和应力分布要比一维效应给出的分布更均匀。

As the best candidate for the high power lasers in next generation, the solid state heat capacity laser (SSHCL) has attracted extensive attention. The principles, power scaling of SSHCL, distributions of fluorescence, temperature in a pumped slab cooling, and slab are presented. The effects of temperature in medium slab on the output power of laser are discussed in detail. Several key points about design are also described.

Based on the fundamental theory of heat transfer, the mathematical formulas that describing the transient temperature distributions of two-sided laser diode (LD) pumped Nd∶GGG (gadolinium gallium garnet) heat capacity slab laser were derived in this paper. By means of finite element analysis by ANSYS, transient temperature fields and stress distribution in the slab medium were simulated with various boundary conditions, while the beam distortions induced by thermal gradients were analyzed briefly. The obtained results could benefit to the primary designing of solid state heat capacity laser (SSHCL). Numerical analysis proved that under incomplete adiabatic boundary conditions, it would result in temperature gradients perpendicular to the optical axis. About 0.2 μm optical path differences would occur between the edge and optical axis of the slab. In addition, the thermal distributions in the slab during the subsequent cooling stage were mainly studied. The influences of different cooling methods such as air cooling, water cooling and mist cooling were discussed and cooling methods suitable for a SSHCL were briefly studied.

The pumping configurations for realizing high average power solid state laser are summarized, including Nd:GGG crystal slab laser in heat capacity operating mode, Yb-doped slab lasers and thin-disk lasers etc., which provide a reference for designing high average power solid state lasers pumping modes.