基于非线性偏振旋转锁模技术的光纤飞秒激光振荡器

基于非线性偏振旋转（nonlinear polarization rotation, NPR）锁模机制的光纤激光器因其结构紧凑、可靠性高而备受关注。基于这一锁模原理设计并搭建了掺镱光纤飞秒激光器。当双向泵浦功率为380 mW，在1 030 nm波段获得了基频重复率为22.8 MHz的锁模脉冲。脉冲宽度为224 fs，平均功率180 mW，单脉冲能量8 nJ,10 dB带宽约为40 nm，信噪比大于50 dB。该激光器采用环形腔结构产生稳定的锁模飞秒脉冲输出，可实现自启动锁模。泵浦功率增加到1.6 W可观察到最高三阶被动谐波锁模，三次谐波对应68.5 MHz重复频率。该激光器由于在线宽、脉宽、脉冲能量上的优势，在光谱测量、拉曼成像等领域具有应用意义。

Femtosecond fiber laser oscillator by nonlinear polarization rotation mode locking technique

Nonlinear polarization rotation (NPR) mode-locked lasers have attracted numerous attention due to their compact structure and high reliability. Based on this mold locking principle, an ytterbium-doped fiber femtosecond laser was designed and built. When the bidirectional pumping power reached 380 mW, the laser was mode-locked with a fundamental frequency repetition rate of 22.8 MHz. The output pulse was centered at 1030 nm with 224 fs for the pulse duration, 180 mW for the average power, 8 nJ for pulse energy, and 40 nm for the bandwidth at 10 dB. The beam had a good quality with signal-to-noise ratio greater than 50 dB. The laser can realize self-start mode locking with a ring laser structure. Besides, the third order passive harmonic mode locking with 68.5 MHz for the repeat frequency was observed by increasing the pump power to 1.6 W. Due to the advantages of line width, pulse width and pulse energy, the laser has application significance in spectral measurement, Raman imaging and other fields.