Quasi-Three-Level Lasers
Quasi-Three-Level Lasers
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DOI：
10.1007/978-1-4615-2998-9_13
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
T. Fan
中科院分区：
文献类型：
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作者：
T. Fan
固体激光器技术复兴的关键发展之一是二极管激光器泵浦源的快速改进。1 - 3相对于固体激光器的灯泵浦，二极管泵浦的一些优点包括更高的总效率、降低增益介质的热负荷、更高的可靠性和更小的尺寸。此外，这两种类型的泵浦源之间还有其他重要的区别。例如，二极管激光器具有更高的光谱和空间亮度，换句话说，二极管激光器输出在光谱上是窄带的，并且它是定向的。其结果是，使用二极管激光泵浦可以实现更高的体积泵浦密度，即使是相对于高功率灯的低功率单条形二极管激光器。高泵浦密度已经导致在室温下的几个跃迁的良好激光性能的证明，这些跃迁在灯泵浦下在室温下仅表现得很差或根本不表现。稀土离子中的这些跃迁包括Nd ~（3+）中0.94 μm附近的4F ~（3/2）-4 I ~（9/2）、Ho ~（3+）中2.1 μm附近的4 - 6的5I ~（7 - 6）-5I ~（8）、Tm ~（3+）中2.0 μm附近的7 - 10的3F ~（4 - 3）H ~（6）、Er ~（3+）中1.5 μm附近的11 - 13的4 I ~（13/2）-4 I ~（15/2）、Yb ~（3+）中1.0 μm附近的2F ~（5/2）-2F ~（7/2）。15、16），如图1所示。这些激光跃迁的共同点是较低的激光能级处于基态多重态，这意味着较低的激光能级仅高于基态几百cm-1。因此，较低的水平有显着的布居在室温下的热平衡，因为在300 K的kT是207 cm-1。这与常见的1.06 µm附近的四能级Nd 3+跃迁形成对比，在300 K时，它具有比基态高出约10 kT的较低能级，因此在热平衡中可以被认为是未填充的，或者红宝石，其中较低的激光能级是基态。在灯泵浦下，这些在基态流形中具有较低能级的激光器通常在低温下工作，以减少热平衡中的较低能级粒子数;在足够低的温度下，这些激光器变成四能级激光器，并获得有效的低阈值性能。
One of the key developments in the renaissance in solid-state laser technology has been the rapid improvement of diode laser pump sources.1–3Some of the advantages of diode-pumping relative to lamp-pumping of solid-state lasers include higher overall efficiency, reduced thermal loading of the gain medium, higher reliability, and reduced size. In addition, there are other important differences between these two types of pump sources. For example, diode lasers have higher spectral and spatial brightness, in other words, the diode laser output is narrowband spectrally, and it is directional. The consequence is that much higher volumetric pumping density can be achieved using diode-laser pumps even with low power single-stripe diode lasers relative to high-power lamps. The high pump densities has led to the demonstration of good laser performance at room temperature of several transitions that performed only poorly or not at all at room temperature under lamp pumping. These transitions in rare-earth ions include the4F3/2-4I9/2near 0.94 µm in Nd3+,4–6the5I7-5I8near 2.1 µm in Ho3+,7–10the3F4-3H6near 2.0 µm in Tm3+,11–13the4I13/2-4I15/2near 1.5 µm in Er3+,13,14and the2F5/2-2F7/2near 1.0 µm in Yb3+(refs. 15, 16) as shown in Fig. 1. The common element in these laser transitions is that the lower laser levels are in the ground-state multiplet which means that the lower laser levels are only a few hundred cm-1above the ground state. Thus the lower levels have significant population in thermal equilibrium at room temperature since kT is 207 cm-1at 300 K. This is in contrast to the common four-level Nd3+transition near 1.06 µm which has a lower level about 10kT above the ground-state at 300 K thus can be considered unpopulated in thermal equilibruim, or ruby in which the lower laser level is the ground-state. With lamp-pumping, these lasers with lower levels in the ground-state manifold were typically operated at cryogenic temperatures to reduce the lower-level population in thermal equilibruim; at sufficiently low temperature these lasers become four-level lasers and efficient, low threshold performance was obtained.