设计了一种使用阵列波导光栅对分布式光纤布喇格光栅中心波长较大范围变化的解调方法.根据阵列波导光栅各通道的中心波长可随温度变化而改变的特性, 通过控制软件循环地在几分钟内使加在阵列波导光栅的芯片温度从30℃线性增加到90℃, 同时用微机高速采集各通道的数据并分别找出各通道数据的最大值时刻所对应的阵列波导光栅芯片温度, 从而根据其波长温度关系在微机上报告此时各光纤布喇格光栅的中心波长.实验结果表明, 系统有效地解决了分布式解调的问题, 微机以小于10 min的周期报告出每通道0.6 nm范围变化的光纤布喇格光栅中心波长(共40个通道), 测量相对误差小于2%.

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.

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.

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.

考虑固体热容激光器对工作介质的要求,对比分析了掺钕的玻璃、YAG和GGG的多种材料性能.并对三者在激光工作周期内的瞬态温度场及热应力进行了数值模拟.结果表明:在给定的边界及工作条件下,当钕玻璃激光器以热容方式工作,时间为5 s时,介质最高升温超过400 K,最大热致应力为25 MPa,接近其断裂极限的50%.在此条件下进行冷却,当水温为283 K时,需经过约120 s才基本恢复到初始工作状态.而Nd:YAG和Nd:GGG两种介质在相同输入工作条件下,工作时间可达10 s,且温度分布相对平坦,温差和热应力较小,经水冷约30 s可恢复到初始状态.但模拟计算中,发现Nd:YAG在冷却阶段的最大应力达77 MPa,已超过断裂阈值下限值的50%.兼顾冷却时间、材料所能承受的应力及晶体生长尺寸,以及实现100 kW的平均功率输出等因素,Nd:GGG晶体是目前三者中比较适合于作为高平均功率、重复率热容方式工作的激光材料.

基于对称双侧激光二极管(LD)抽运Nd∶GGG(掺钕钆镓石榴石)激光晶体板条,从热传导基本方程出发,以废热等效于内热源模型为前提, 利用有限元分析软件ANSYS对Nd∶GGG板条在热容工作下的瞬态温度场及应力场进行了数值模拟,分析了在不同边界条件下温度和应力随时间和空间的变化特性及其热致变形。计算结果表明：在激光发射阶段,边界非绝热使得板条在垂直光轴方向产生温度梯度,由此产生的折射率梯度和应力梯度导致距离光轴最远的板条边缘和光轴处产生约0.2 μm的变形量。同时模拟了冷却阶段空气对流冷却、水循环冷却及喷雾冷却条件下的温度变化过程,研究了适用于热容板条固体激光器工作的冷却手段。

固体热容激光器(SSHCL)作为下一代最佳候选高功率激光器, 引起人们广泛关注。介绍了固体热容激光器工作原理、光抽运期间介质板内荧光分布和温度分布、介质板冷却以及功率标定。详细讨论了激光介质温度对激光输出功率的影响, 对有关设计要点也作了相关分析。