朗琴尺可用于快速精确地测量高斯光束的直径。本文介绍一种朗琴测量法的理论分析。其在理论上的主要结果是光束直径与被测参数(P_(max)与 P_(min))之间的一个很简单的关系式。将此方法同常用的针孔、狭缝及刀口法加以比较,讨论了朗琴方法的主要优点,给出了这种方法在应用上的一些注意事项。 Long strings can be used to quickly and accurately measure the Gaussian beam diameter. This article describes a theoretical analysis of the Long Qin measurement method. The main theoretical result is a very simple relationship between the beam diameter and the measured parameters (P max and P min). This method is compared with the commonly used pinholes, slits and knife-edge method, discusses the main advantages of the Longqin method, and gives some considerations on the application of this method.