为实现光纤激光器径向偏振光的高效输出, 提出并搭建了基于液晶聚合物(LCP)的纳秒脉冲掺镱(Yb)主振荡器功率放大(MOPA)系统。该系统采用空间相位转换法, 利用LCP涡旋半波片将全光纤MOPA激光器输出的高峰值功率、窄线宽、线偏振、高斯形分布的纳秒脉冲信号转换为横向强度呈空心环状分布的拉盖尔-高斯光。MOPA激光器系统由窄线宽连续种子源、电光强度调制器和后续的5级YDF放大器组成, 通过实验获得了20.1 W的稳定LP01模输出。而后的LCP涡旋波片用作空间模式转换器, 最终获得的平均输出功率为19.5 W, 脉宽为10 ns, 重复频率为10 kHz, 横向剖面呈规则空心环形的径向偏振光输出, 模式转换效率可达97%。另外, 通过PBS测量法测得径向偏振光的模式纯度约为88.5%, 兼具高功率与高纯度的优势。

This study demonstrates the use of a Liquid Crystal Polymer (LCP) vortex retarder-based Yb-Doped Fiber (YDF) MOPA system with nanosecond pulse output to achieve efficient generation of a radially polarized beam from fiber lasers. The LCP vortex half-wave plate was employed as a mode converter after the MOPA laser to efficiently convert the high-peak-power, narrow-linewidth, linearly polarized nanosecond Gaussian pulse signal into a Laguerre-Gaussian beam with a hollow-ring distribution of transverse intensity using the spatial phase conversion method. When the MOPA system consisted of a narrow-linewidth continuous seed source, an electro-optical intensity modulator and a five-stage YDF amplifier were built up. A stable LP01 mode output with an average power of 20.1 W was obtained from the MOPA system. Subsequently, an LCP vortex half-wave plate was adopted as a spatial mode converter and a radially polarized beam output with a maximum average output power of 19.5 W, pulse width of 10 ns, and perfect hollow-ring transverse intensity was obtained at a repetition rate of 10 kHz. The mode purity measured by the PBS method is about 88.5%, which indicates that the radially polarized beam obtained has the advantages of high efficiency and high mode purity. This work can establish the foundation for the practical and highly efficient applications of radially polarized beams in the field of optical trapping, high-resolution imaging, and materials processing.