Abstract: When we use the laser image method to measure the deflection，the case whether the laser transmitter can automatically adjust the level，the length of adjusting time and the size of the projected spot have direct impact on the accuracy of the deflection monitoring. So，a laser system of self-adjusting level for deflection monitoring is designed. Gravity pendulum is used for self-adjusting. Through the analysis of stress and trajectory of the gravity pendulum，critical damping conditions are used to determine damping coefficients and to adjust the electromagnetic damper magnetic induction intensity and the drag coefficients，which finally realize rapid hovering. In order to maintain good concentration of energy when laser is shooed in long distance，Fermat Theorem is used to design the corresponding focusing lenses，which are combined with the Galileo beam expander to compose the laser lens to realize long distance shoot. The laser lens parameters and the electromagnetic damper parameters are obtained after analyzing and deducing. The achievement provides theoretical foundation for the appearance of the real laser emission device.

Key words: self-adjustinglevelbygravity, criticaldampingconditions, reluctancedamper, beamexpander, Fermat＇sprinciple, focusinglens

摘要： 激光图像法测量挠度时激光发射装置能否自动安平、安平时间长短、投射光斑的大小都直接影响挠度测量的 准确性，为此设计了一种自安平挠度激光发射系统。该系统采用重力摆的方式实现激光装置自安平，通过对重力摆 受力及运动轨迹分析，利用临界阻尼条件确定阻力系数，调节磁阻尼器磁感应强度与阻力系数匹配实现系统快速悬 停;为了保持远距离投射时激光仍具有良好的能量集中度，通过费马原理设计相应的聚焦镜，并与伽利略扩束系统 组成激光镜头，实现激光的远距离投射。经过分析推导得出电磁阻尼器相应参数和激光镜头参数，为具体激光发射 装置实现提供了理论基础。

关键词: 重力安平, 临界阻尼条件, 磁阻尼器, 扩束系统, 费马原理, 聚焦镜