We report for the first time, to the best of our knowledge, graphene mode-locked operation of a femtosecond Alexandrite laser at 750 nm. A multipass-cavity configuration was employed to scale the output energy and to eliminate spectral/$Q$-switching instabilities. By using a monolayer graphene saturable absorber, mode locking could be obtained. With 5 W of pump at 532 nm, nearly transform-limited, 65 fs pulses with a time-bandwidth product of 0.319 were generated. The mode-locked laser operated at a pulse repetition rate of 5.56 MHz and produced 8 mW output power, corresponding to a pulse energy and peak power of 1.4 nJ and 22 kW, respectively. These experiments further show that graphene can be used to initiate mode locking at wavelengths as low as 750 nm.

中文翻译：

---

石墨烯锁模飞秒亚历山大石激光器

据我们所知，我们首次报告了飞秒亚历山大石英激光器在750 nm处的石墨烯锁模操作。采用多通道腔配置来缩放输出能量并消除频谱/$问$-切换不稳定性。通过使用单层石墨烯可饱和吸收剂，可以获得锁模。在532 nm处泵浦功率为5 W时，产生了几乎受变换限制的65 fs脉冲，时间带宽积为0.319。锁模激光器以5.56 MHz的脉冲重复频率工作，并产生8 mW的输出功率，分别相当于1.4 nJ的脉冲能量和22 kW的峰值功率。这些实验进一步表明，石墨烯可用于启动低至750 nm波长的锁模。