Freiberg R J, Halsted A S
Appl Opt. 1969 Feb 1;8(2):355-62. doi: 10.1364/AO.8.000355.
A study has been conducted to determine the trade-offs among beam divergence, output power, and mirror alignment tolerances of high power argon ion lasers operating in various low order transverse modes. The radial intensity distribution and angular divergence of the actual laser modes from the active cavity have been measured and are compared with the theoretical passive cavity modes. The intensity distributions of higher order laser modes are found to differ markedly from those predicted by theory. The differences consist primarily of enhancement of the intensity of the off-axis peaks relative to that of the center peaks. These differences are caused by the relative high small-signal gain and the saturable gain characteristics of the medium. The beam divergence in free space of different transverse modes agrees very closely with that predicted for the passive cavity modes. The three lowest order transverse modes (i.e., TEM(00), TEM(01*), and TEM(10)) diverge at 1.1, 2.4, and 3.6 times the rate of a diffraction limited gaussian beam having the same diameter at the 1/e(2) intensity points. The mirror alignment tolerances associated with different transverse modes have been measured for both double concave and plano concave cavity configurations using a wide variety of spherical mirrors. For a given cavity configuration, as the order of the transverse mode increases, the alignment requirements become progressively less stringent. In accordance with theory, the alignment tolerances are found to be less severe for double concave cavities than for plano concave cavities. For a given cavity configuration, higher order transverse modes have a larger beam diameter and consequently couple to a larger volume of the laser medium. Therefore, a greater power output may be obtained in a given length by using a higher order transverse mode. Data on the relative power available in different transverse modes as a function of cavity configuration are given. A knowledge of the trade-offs among beam divergence, cavity stability, and power output for different transverse modes allows the optimum transverse mode and cavity configuration for a given laser application to be selected.
已开展一项研究，以确定在各种低阶横向模式下运行的高功率氩离子激光器在光束发散、输出功率和镜对准公差之间的权衡。已测量了有源腔中实际激光模式的径向强度分布和角发散，并与理论无源腔模式进行了比较。发现高阶激光模式的强度分布与理论预测有显著差异。这些差异主要包括离轴峰值强度相对于中心峰值强度的增强。这些差异是由介质相对较高的小信号增益和饱和增益特性引起的。不同横向模式在自由空间中的光束发散与无源腔模式的预测非常接近。三个最低阶横向模式（即TEM(00)、TEM(01*)和TEM(10)）的发散率分别是在1/e(2)强度点具有相同直径的衍射极限高斯光束的1.1、2.4和3.6倍。使用各种球面镜，针对双凹腔和平凹腔配置测量了与不同横向模式相关的镜对准公差。对于给定的腔配置，随着横向模式阶数的增加，对准要求逐渐变得不那么严格。根据理论，发现双凹腔的对准公差比平凹腔的更宽松。对于给定的腔配置，高阶横向模式具有更大的光束直径，因此耦合到更大体积的激光介质中。因此，通过使用高阶横向模式，在给定长度内可以获得更大的功率输出。给出了不同横向模式下相对可用功率与腔配置的函数关系数据。了解不同横向模式在光束发散、腔稳定性和功率输出之间的权衡，有助于为给定的激光应用选择最佳的横向模式和腔配置。
