We report on the direct generation of passively mode-locked vortex lasers in the visible spectral region, for the first time to the best of our knowledge, using a Pr:LiYF4 (Pr:YLF) crystal as the gain medium. A stable mode-locked TEM00 mode has been achieved with a maximum average output power of 75 mW using a graphene saturable absorber mirror. The mode-locked pulse width is measured to be as short as about 73.4 ps at a repetition rate of about 140 MHz, and the laser wavelength is at about 721 nm with spectral width of about 0.5 nm. By slightly misaligning the laser resonator, a first-order Laguerre-Gaussian mode (LG0,1) has also been obtained with output power reduced to about 22 mW. The achieved LG0,1 mode has been verified via a home made improved Fizeau interferometer. This work provides a simple and universal method for direct generation of an ultrafast vortex laser, which can be readily extended to other spectral regions by using different laser gain mediums.

中文翻译：

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在基于 CVD 石墨烯的被动锁模 Pr:LiYF4 可见激光器中直接产生超快涡旋光束

我们报告了在可见光谱区域直接生成被动锁模涡旋激光器，据我们所知，这是第一次使用 Pr:LiYF4 (Pr:YLF) 晶体作为增益介质。使用石墨烯可饱和吸收镜实现了稳定的锁模 TEM00 模式，最大平均输出功率为 75 mW。在大约 140 MHz 的重复频率下，测得锁模脉冲宽度短至大约 73.4 ps，激光波长大约为 721 nm，光谱宽度大约为 0.5 nm。通过稍微错位激光谐振腔，还获得了一阶拉盖尔-高斯模式 (LG0,1)，输出功率降低到约 22 mW。实现的 LG0,1 模式已通过自制的改进 Fizeau 干涉仪进行了验证。