设计了一种用于大型复杂激光器的紧凑空间中实现在线监测光是否恰好通过空间滤波器小孔光阑中心的检测方法。紧贴空间滤波器小孔光阑上方的窗口片胶合一棱镜,使置于CCD前的LED发出的光经棱镜后照射到小孔光阑,反射回的图像由CCD接收,从而实现在线监测。分析了所需棱镜应满足的条件:棱镜尖角到小孔光阑中心的垂直距离不小于4 mm,棱镜的角度应尽量小以致照射小孔光阑的出射光尽可能平行。并利用光学设计软件Zemax模拟了加入棱镜后的光路,合理的棱镜参数为角度55°,两直角边分别为10 mm和14.3 mm。实验验证了所设计方法的高效可行性。

对侧面抽运模块的抽运结构进行了优化,采用漫反射腔设计,利用3个激光二极管阵列(LDA)旋转对称抽运尺寸为2 mm×75 mm,掺杂原子数分数为4%的钕玻璃棒。钕玻璃棒两端面镀有在1053 nm高透率为99.8%的增透膜,为消除放大的自发辐射(ASE)光振荡,钕玻璃两端面采用1.5°倾角设计。放大器采用集体制冷,产生的热量由在热沉中流动的去离子水带走。能量10 μJ,工作频率1 Hz,脉冲宽度3 ns,输出波长1053 nm的种子激光经过钕玻璃放大器后,在抽运功率为8.2 kW,抽运脉冲宽度为400 μs时达到了70倍的稳定高增益,放大器的荧光分布均匀,脉冲波形图放大后无畸变。

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.

Approximate formulas of transient temperature and stress distributions in the slab of a two-side pumped heat capacity laser are attained by solving the heat diffusion equation. Based on the formulas, the distributions of temperature and stress during the pump period of a two-sided symmetrically laser diode array (LDA) pumped Nd:GGG slab laser with 5-kW average output power are numerically simulated. The results show that the temperature in the slab will averagely increase by more than 70 Celsius degrees after operating for 10 seconds; the stress and maximum of the temperature difference in the slab are about 30 MPa and 24 Celsius degrees, respectively. The thermal induced effects are discussed also.

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.

Considering some necessary factors in the design of SSHCL, material properties of Nd doped glass, YAG and GGG were compared. Transient temperature fields and thermal stress in these slab mediums during one working cycle were simulated. Numerical analysis results showed that the internal external temperature difference in a neodymium doped glass slab was 75 K and the peak temperature value was 400 K when pumping time arrived 5 s. The maximum stress came to 50% of glass fracture limit. During subsequent water cooling period, the initial state was recovered after 120 s. On the same boundary conditions, Nd:YAG and Nd:GGG slabs could maintain relatively smooth temperature profile while the temperature rising and equivalent thermal stress were lower compared to glass. In later cooling phase, both of them could reach their operating commencement within 30 s. As cooling, the maximum stress of Nd:YAG overran 50% of the stress limit, thus increasing its tendency to fracture. Taken cooling time, fracture limit and obtainable size of the crystal into account, Nd:GGG should be the suitable active medium for high average power, repetitive frequency heat capacity laser.