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飞秒光频梳的任意长绝对测距*
Arbitrary and absolute length measurement based on femtosecond optical frequency comb
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摘要: 高精度测距在工业、航空航天、科学研究等方面都具有重要应用，而不断发展的激光测距技术始终处于前沿研究领域.本文研究飞秒光频梳绝对测距技术，拓展光梳在长度测量领域的应用.在利用脉冲激光进行任意绝对长度测量中常用到飞行时间法，然而其测量分辨力受限于电子器件的带宽，仅为毫米量级.为克服这一缺点，本文研究了光梳多脉冲序列之间的时间相干性，结合多脉冲序列干涉法和飞行时间法提出了任意长绝对测距的方法，搭建了基于改进型Michelson干涉原理的任意绝对测长系统，通过同时测量多脉冲序列的一阶和二阶互相关信号，可以分别计算出飞行时间的时间差，即可得到被测距离.利用光梳作为光源进行了0.6 m的绝对测距实验，将测量结果与高精度激光位移传感器的测量值进行比较，实验结果表明本系统具有良好的测量线性度，并且测距精度可达±0.5μm.Abstract: High-accuracy distance measurement plays an important role in many applications, such as industry measurement, Aerospace and scientific research. The continual development oflaser ranging technique is always a frontier topic of geometric measurement, therefore this paper develops the application of femtosecond optical frequency comb for length measurement. Time-of-flight principle for distance measurement is widely used by pulse laser, however, achievable resolution reaches only a few millimeters at best due to the limited bandwidth of electronics. In this paper, the temporal coherence of multiple pulse train is analyzed, and an arbitrary and absolute length measurement system is set up based on modified Michelson interferometer by combining multiple pulse train interference and time-of-flight method. The timing difference is separately calculated by the first-order and second-order optical cross-correlation signals, therefore the absolute distance is calculated. An experiment is conducted by measuring a 60 cm length, and the measurement result is compared with a high precision laser displacement sensor. The result shows a good measuring linearity, and the measurement precision of ±0.5 μm is achieved.
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