THz频差可调谐双频固体激光绝对距离干涉测量技术研究

In order to effectively solve the problem of precision measurements of large size workpieces in the field of mechanical manufacturing, the absolute-distance interferometry will be investigated in this project, using a dual-frequency solid-state laser with tunable frequency-difference up to terahertz level. A diode-pumped two-cavity dual-frequency Yb:KGW laser at wavelength region of 1030nm is designed, each cavity of which contains a pair of Fabry-Perot etalons, ensuring the p-polarized light in the linear cavity and the s-polarized light in the right angle cavity to oscillate simultaneously in single longitudinal mode, so that an orthogonally and linearly polarized dual-frequency laser can be output. In order to tune the frequency-difference of the dual-frequency laser in a range of approximately 1GHz~5THz, the relationship between the frequency-difference and the tilting angles of the intra-cavity Fabry-Perot etalons will be investigated experimentally. The technique of digital Pound-Drever-Hall frequency stabilization being used, the dual-frequency laser will be stabilized to two different resonant frequencies of single referrence of Fabry-Perot cavity, with a frequency-difference stability of better than 30kHz. The dual-frequency solid-state laser with tunable and stable frequency-difference being used as a light source, a super-heterodyne absolute-distance interferometric system capable of calibrating the synthetic wavelength is designed, and a measurement uncertainty of better than 0.15ppm will be obtained in an absolute-distance range of 0.05m~50m when the stage-by-stage refined measurement method of multi-stage synthetic wavelengths is employed.

为了有效解决机械制造等领域的大尺寸工件精密测量问题，本项目拟研究太赫兹（THz）频差可调谐双频固体激光绝对距离干涉测量技术，设计一种二极管泵浦1030nm波段双腔双频Yb:KGW激光器，每个腔内包含一对Fabry-Perot标准具，使直线腔内的p偏振光和直角腔内的s偏振光同时以单纵模振荡，实现正交线偏振双频激光输出；实验研究双频激光频差随腔内Fabry-Perot标准具倾角之间的关系，获得1GHz~5THz频差调谐范围；采用数字Pound-Drever-Hall稳频技术，将双频激光稳定在同一台Fabry-Perot参考腔的两个不同谐振频率处，频差稳定性优于30kHz；以这种频差可调谐和频差稳定的双频固体激光器作光源，设计一种能够标定合成波长的超外差干涉绝对距离测量系统，应用多级合成波长逐级精化测量法，在0.05~50m绝对距离范围内的测量不确定度优于0.15ppm。

大频差可调谐双频稳频全固态激光器是合成波绝对距离干涉测量系统的理想光源。本项目开展了大频差可调谐双腔双频全固态激光器振荡原理与关键技术研究，主要包括THz频差可调谐双腔双频全固态激光器、F-P标准具选模双腔双频Nd:YAG激光器、双腔双频Nd:YAG激光器频差稳定系统、以及双腔双频Nd:YAG激光器合成波绝对干涉测距系统的理论设计及实验研究；从实验上分别获得了1030nm和1064nm正交线偏振大频差可调谐双频激光同时振荡，其最大频差分别达到1.4THz和76GHz，研制成功1064nm波段24GHz频差正交线偏振双腔双频Nd:YAG激光器样机；设计了两种基于双调制器和单调制器正交解调Pound-Drever-Hall（QD-PDH）方法的双腔双频Nd:YAG激光器频差稳定系统，实验获得的频差稳定性分别优于4.2×10(-7)和2.9×10(-7)；以单调制器QD-PDH稳频1064nm波段24GHz频差双腔双频Nd:YAG激光器作光源，设计并建立了合成波长标定与绝对距离外差干涉测量实验系统，实验标定了空气中的合成波长，其平均值及标准差分别为12.4614mm和0.13μm；重复测量了900mm被测绝对距离，其测量平均值及标准差分别为899.3855mm和1.36μm，相对测量不确定度为4.54×10(-6)。研究结果表明：采用频差大于0.1~1.4THz的QD-PDH稳频双腔双频全固态激光器作为绝对干涉测距系统的光源，可以实现相对测量精度优于10(-7)量级的超精密绝对距离测量。