Wagner Gerd, Wulfmeyer Volker, Behrendt Andreas
Institute of Physics and Meteorology, University of Hohenheim, Garbenstrasse 30, 70599 Stuttgart, Germany. Gerd.Wagner@uni‐hohenheim.de
Appl Opt. 2011 Nov 1;50(31):5921-37. doi: 10.1364/AO.50.005921.
Differential absorption lidar (DIAL) is a unique technique for profiling water vapor from the ground up to the lower stratosphere. For accurate measurements, the DIAL laser transmitter has to meet stringent requirements. These include high average power (up to 10 W) and high single-shot pulse energy, a spectral purity >99.9%, a frequency instability <60 MHz rms, and narrow spectral bandwidth (single-mode, <160 MHz). We describe extensive modeling efforts to optimize the resonator design of a Ti:sapphire ring laser in these respects. The simulations were made for the wavelength range of 820 nm, which is optimum for ground-based observations, and for both stable and unstable resonator configurations. The simulator consists of four modules: (1) a thermal module for determining the thermal lensing of the Brewster-cut Ti:sapphire crystal collinear pumped from both ends with a high-power, frequency-doubled Nd:YAG laser; (2) a module for calculating the in-cavity beam propagations for stable and unstable resonators; (3) a performance module for simulating the pumping efficiency and the laser pulse energy; and (4) a spectral module for simulating injection seeding and the spectral properties of the laser radiation including spectral impurity. Both a stable and an unstable Ti:sapphire laser resonator were designed for delivering an average power of 10 W at a pulse repetition frequency of 250 Hz with a pulse length of approximately 40 ns, satisfying all spectral requirements. Although the unstable resonator design is more complex to align and has a higher lasing threshold, it yields similar efficiency and higher spectral purity at higher overall mode volume, which is promising for long-term routine operations.
差分吸收激光雷达（DIAL）是一种用于从地面到平流层下部进行水汽剖面测量的独特技术。为了进行精确测量，DIAL激光发射器必须满足严格的要求。这些要求包括高平均功率（高达10 W）和高单脉冲能量、光谱纯度>99.9%、频率不稳定度<60 MHz均方根值以及窄光谱带宽（单模，<160 MHz）。我们描述了为在这些方面优化钛宝石环形激光器的谐振器设计所做的大量建模工作。针对820 nm的波长范围进行了模拟，该波长范围对于地面观测是最佳的，并且针对稳定和非稳定谐振器配置都进行了模拟。模拟器由四个模块组成：（1）一个热模块，用于确定用高功率倍频Nd:YAG激光从两端共线泵浦的布儒斯特切割钛宝石晶体的热透镜效应；（2）一个用于计算稳定和非稳定谐振器腔内光束传播的模块；（3）一个用于模拟泵浦效率和激光脉冲能量的性能模块；（4）一个用于模拟注入种子和激光辐射光谱特性（包括光谱杂质）的光谱模块。设计了一个稳定的和一个非稳定的钛宝石激光谐振器，以在250 Hz的脉冲重复频率和大约40 ns的脉冲长度下提供10 W的平均功率，满足所有光谱要求。尽管非稳定谐振器设计在对准方面更复杂且具有更高的激光阈值，但它在更高的总体模体积下产生相似的效率和更高的光谱纯度，这对于长期常规操作很有前景。
