We demonstrate a high pulse energy and low pulse rate 2 µm femtosecond fiber laser potentially applicable to laser surgery and vehicle laser detection and ranging. The laser is configured by a half kilometer long all-fiber ring cavity with two thulium-doped fiber gains deployed separately and is hybrid mode-locked by the coaction of a graphene saturable absorber and nonlinear polarization rotation. Numerical simulations were carried out to back up the mode-locking stability and estimate the maximally extractable pulse energy. We achieved a pulse energy of about 54.6 nJ, to the best of our knowledge the highest as a seed femtosecond pulse, and a pulse rate of 427 kHz, the lowest ever reported. The pulse duration was about 456 fs as measured by an intensity autocorrelator, and the output optical spectrum showed a wide FWHM of about 51.7 nm. We also examined the stability of the laser output over tens of hours.

我们展示了高脉冲能量和低脉冲速率的2 µm飞秒光纤激光器，可能适用于激光手术以及车辆激光检测和测距。该激光器由一个半公里长的全光纤环形腔构成，具有分别部署的两个掺-光纤增益，并且通过石墨烯可饱和吸收剂和非线性偏振旋转的共同作用被混合锁模。进行了数值模拟以支持锁模稳定性并估计最大可提取脉冲能量。我们获得了大约54.6 nJ的脉冲能量，据我们所知，它作为种子飞秒脉冲最高，脉冲频率为427 kHz，是有史以来最低的。通过强度自相关器测量的脉冲持续时间约为456 fs，输出光谱显示出约51.7 nm的宽FWHM。