基于扫频采样的飞秒激光大尺寸测距方法研究

Study on the Large-Scale Distance Measurement Method for Femtosecond Laser Based on Frequency Scanning and Optical Sampling

作为一种高精度测量工具,飞秒激光具有优于传统激光技术的特性,已被广泛应用于工业生产、航空航天、科学研究等领域。扫频采样法在很大程度上改善了机械振动、扫描速度过慢等问题,对飞秒激光的绝对测距性能提升有着重要的意义。基于扫频采样原理,提出了一种利用飞秒激光的大尺寸距离测量方法,并对该技术的测量原理、干涉光谱和解调算法等方面进行了研究。首先,根据飞秒激光的锁模生成原理和压电陶瓷的压电效应,介绍了飞秒激光器连续扫描重复频率的方法。在此基础上,结合传统的光学采样法原理,解释了扫频采样法的测距原理,推导并讨论了光纤延迟线的长度对扫描距离的影响。然后,搭建了基于扫频采样的飞秒激光测距系统,在线性导轨上进行了远距离的测量实验,同时设计了基于迈克尔逊干涉原理的He-Ne激光参考光路。根据实验环境修正了空气群折射率,分析了测量距离对光谱条纹峰值和宽度的影响,测量了不同目标位置处的激光扫描距离。在50.4m的测量范围内,扫描距离从0.56mm增加到1.12mm,充分验证了光纤延迟线对提升大尺寸测距能力的重要性。周期性的频率扫描可产生互相关条纹,通过对测量光谱条纹进行希尔伯特变换处理,解算出实时的频率变化量和采样倍乘系数,从而获取被测的距离信息。此外,为了减小系统的时间延迟误差,提高测量的准确性,采用差分原理对算法进行了改进。在希尔伯特算法基础上,分别对频率和距离进行差分处理,解算距离信息。实验结果表明,经过对比,采用基于距离差分的改进算法处理数据,性能结果较好。算法改进后,系统在50m范围内的测量精度从11μm提高到4μm,相对精度从2.2×10^-9提高到8×10^-8,测距准确性明显提高。通过分析重复性测量数据,并与增量式激光干涉仪结果比对,测量误差的标准差从10μm提高到2μm,最大相对稳定性从2×10^-9提高到4×10^-8,测距稳定性明显提高。因此,该方法有较为优秀的大尺寸测距能力,具有同时实现高精度、大尺寸、快速绝对测距的潜力,在未来的精密光谱测量领域有着很大的前景。

As a high-precision measurement tool, femtoseco nd laser is superior to traditional laser technology and has been widely use d in industrial production, aerospace, scientific research and other fields. The method of frequency sweeping and optical sampling has greatly improved mech anical vibration and slow scanning speed, which has great significance for impro ving the absolute ranging performance of femtosecond laser. A large-scale dista nce measurement method using femtosecond laser is proposed based on the principl e of frequency sweeping and optical sampling, and research is performed on the m easurement principle, interference spectrums and demodulation algorithm of this technology. Firstly, according to the generation principle of mode-locked femto second laser and the piezoelectric effect of piezoelectric ceramics, the method of continuous scanning repetition frequency of femtosecond laser was introduced. On this basis, the traditional optical sampling principle was used to explain t he range measurement principle of optical sampling method, and the influence of the fiber delay line length on the scanning range was deduced and discussed. The n, a distance measurement system using femtosecond laser was set up, long distan ce measurement experiments were carried out on a linear guide, and the He-Ne re ference light path based on Michelson interference principle was designed. The g roup refractive index of air was modified according to the experimental environm ent, the influence of measured distance on the spectrum of interference fringes was analyzed, and the scanning ranges at different target positions were measure d. In the range of 50.4 m, the scanning range increased from 0.56 to 1.12 mm, and it fully proved the importance of fiber delay line for improving large-sca le ranging capabilities. Periodic scanning frequency could generate cross-corre lation fringes, the real time frequency variations and sampling multiplication f actors were calculated by performing Hilbert transform processing on the interfe rence spectrums, and the distance information was obtained. In addition, in orde r to reduce the time delay error of the system and improve the accuracy of the m easurement, the difference principle was used to improve the algorithm. The expe rimental results show that, by co ntrast, the improved algorithm based on distance difference is used to process d ataand the performance results are better. After the algorithm is improved, the measurement accuracy of the system is improved from 11 to 4 μm in the range of 50 m, and the relative accuracy is improved from 2.2×10^-9 to 8×10^-8 , which indicates that the accuracy is significantly improved. The repeatabi lity measurement data is analyzed and compared with the results of incremental l aser interferometers, the standard deviation of measurement error is improved f rom 10 to 2 μm, and the maximum relative stability is improved from 2×10^-9 to 4×10^-8 , which indicates that the stability is significantly impro ved. Therefore, the method has excellent capability of large-scale distance m easurement, the potential of achieving high-accuracy, large-scale and fast ab solute range measurement simultaneously, and great prospects in the field of pr ecision spectrum measurement in the future.