基于飞秒激光多普勒效应的流速传感新方法

Ocean observation is the foundation for marine science study, ocean current is the most significant observing element due to its influence on the transportation of global material, energy, and heat. Due to the low-flow characteristics of ocean currents, the current velocity sensing methods hardly improve the measurement accuracy. In this study, the femtosecond laser is introduced into the ocean current measurement. By using the high repetition frequency stability which benefits from the femtosecond laser property that the repetition frequency can be connected to the microwave frequency standard, it is possible to innovate a velocity sensing method which not only has a high sensing accuracy but also a broad sensing range. In this study, a full play to the advantages of femtosecond laser light source is taken into consideration. Getting rid of the convent optical frequency heterodyne and optical frequency direct detection methods, a microwave frequency direct detection method is adopted which directly project the femtosecond laser plate into the flow field to generate optical scattering signals with high quality, and then receive the signals from multi-directions for discriminator processing in microwave frequency domain. Based on this detecting methods, the needs for velocity direction and profile measurement is considered. Borrowing the scanning way of an earth wind field detection lidar, a measuring equipment is studied which supports multiple receivers’ cooperative scanning measurement. Based on these work, the flow velocity sensing method using the femtosecond laser repetition frequency Doppler effect is realized. Around this goal, the femtosecond laser repetition frequency Doppler effect is studied from the theoretical point of view, and the cooperative scanning control method is studied from the technical point of view, then an experiment platform is setup for verifying the proposed method.

海洋观测是进行海洋科学研究的基础，海流因影响全球物质、能量、热量的输运成为最重要的观测要素。因海流本身的低流速特征，现有传感方法很难在测量精度方面有所提高。本课题尝试将飞秒激光引入流速测量，利用飞秒激光重频可锁定到微波频标的高稳定度性质，使兼具高精度和宽量程的流速传感成为可能。本课题传感方法的研究充分考虑发挥飞秒激光光源优势，摆脱传统光频外差和光频直接探测方法框架，将采用飞秒激光光片直射流场以获取高质量散射光信号，接收端从多散射方向接收光信号进行微波频域（重频）鉴频处理的直接探测方式。在此探测方式基础上，考虑流速方向及分布测量需求，借鉴地球风场探测气象雷达扫描测量思想，研究多接收体协同快速扫描测量装置，实现基于飞秒激光重频多普勒频移原理的流速传感新方法。围绕此目标，从理论上研究飞秒激光重频的多普勒频移原理，从技术方法上解决多接收体扫描测量机构时空协同控制方法问题，搭建平台验证新方法。

研究了基于飞秒激光重复频率多普勒效应的流速测量方法，主要成果包括：理论分析推导了飞秒激光重复频率多普勒效应公式，仿真和实验验证了理论分析的正确性；进一步依据测距原理通过相位测速法在测量方法层面进行算法研究和实验验证，实验结果突显了飞秒激光测速的精度优势；通过连续光法、相位测速法、光纤法、迈克尔逊干涉法、双光梳法等方法的探索性验证，双光梳法在数据获取速度、精度保证等方面优势明显；自行搭建了双光梳集成光源，并进行了测速实验，与精密移动导轨和标准流量计比较，结果吻合。扩展性开展水下声速测量研究，提出光梳干涉和声光效应相融合的水下声速测量方案，并进行了实验验证，结果与商用声速仪对比，有明显精度优势。在流速等关键海洋参数的计量方法上，积累了重要工作基础。