超短超强激光系统作为研究强场物理、超快现象的重要手段受到广泛关注。钛宝石晶体具有超宽发射光谱（650nm-1100nm），因此被广泛应用于飞秒激光脉冲的产生。再生放大器作飞秒激光系统的初级放大器，具有高稳定、高光束质量、高效率的优势，同时目前研究目标也定位在更短脉宽、更高重频及更高功率。为了实现高功率的激光输出往往会采用高功率泵浦，因此不可避免地会产生温度梯度、热应力、热致双折射等热效应，严重的热效应会引起放大效率降低、光束质量变差、腔型失谐，光学元件损坏等一系列问题。论文针对钛宝石激光晶体的热效应，对再生放大器输出功率和工作稳定性的提升开展了系列的数值模拟和实验验证，可为高功率飞秒激光器的稳定运行提供了一定的设计准则。本文针对再生放大器中布儒斯特角切割的钛宝石板条晶体的热效应开展了数值模拟和实验研究。1）利用有限元方法，通过求解传热方程模拟晶体的温度分布、光程差与热焦距。通过改变不同物理量模拟晶体温度分布的变化从而找到减小热效应的有效方式；2）使用波前探测器测量He-Ne探针光穿过晶体的波前相位变化，测量了不同泵浦功率下的晶体热焦距，测量的结果与模拟相吻合。通过对晶体热效应的数值模拟和实验测量，为提高激光器输出功率、优化光斑质量提供了参考数据。3）对环形再生腔的输出展开了实验研究，对环形再生腔中钛宝石的散热处理做了一些初步的实验尝试。使用半导体制冷装置将再生腔中的钛宝石晶体温度冷却至-20℃，实现了10.3W功率、1kHz重复频率的脉冲输出且可以保持长时间稳定运行；之后对钛宝石键合晶体进行了实验测试，初步验证了钛宝石键合晶体工作的可行性。
The ultra-intense and ultra-short laser-pulse system has been widely concerned as an important method for studying strong field physics and ultrafast phenomena. Ti:sapphire crystal has a wide emission spectrum(650nm-1100nm), so it is widely used in femtosecond laser pulse generation. As the primary amplifier of femtosecond laser system, regenerative amplifier has the advantages of high stability, high beam quality and high efficiency. At the same time, the current research target of regenerative amplifier is located in shorter pulse width, higher repetition rate and higher power. High-power pump is often used in order to achieve high-power output, which will inevitably produce temperature gradient, thermal stress, thermally induced birefringence etc. Serious thermal effects will cause a series of problems such as low amplification efficiency, poor beam quality, cavity detuning, optical element damage and so on. Aiming at the thermal effect of Ti:sapphire laser crystal, a series of numerical simulation and experimental verification are carried out to improve the output power and working stability of regenerative amplifier, which can provide certain design criteria for the stable operation of high-power femtosecond laser.In this paper, the thermal effect of Brewster-cut Ti:sapphire slab crystal in regenerative amplifier is studied by numerical simulation and experiment. 1) The temperature distribution, optical path difference and thermal focal length of the crystal are simulated by solving the heat transfer equation with the finite element method. The effective ways to reduce the thermal effect are found by changing different physical quantities to simulate the change of crystal temperature distribution; 2) The wavefront sensor is used to measure the phase change of the He-Ne probe beam passing through the crystal, and thermal focal length of the crystal under different pump powers is measured. The measured results are consistent with the simulation. The reference data are provided for improving the laser output through the numerical simulation and experimental measurement of the thermal effect of Ti:sapphire crystal. 3) The output of the ring regenerative amplifier is studied experimentally, and some preliminary experiments are made on the heat dissipation of Ti:sapphire in the ring regenerative amplifier. The temperature of Ti:sapphire crystal in the ring regenerative amplifier is cooled to - 20 ℃ by using Thermo-electric cooling. The maximum output power of the regenerative amplifier is 10.3W and the pulse repetition rate is 1kHz, and it can keep stable operation for a long time. Afterwards, experimental test is carried out on the composite Ti:Sapphire crystal, which initially verifies the feasibility of the composite Ti:Sapphire crystal.
