Qiao Zhen, Kong Lingchen, Xie Guoqiang, Qin Zhipeng, Yuan Peng, Qian Liejia, Xu Xiaodong, Xu Jun, Fan Dianyuan
Opt Lett. 2017 Jul 1;42(13):2547-2550. doi: 10.1364/OL.42.002547.
Femtosecond optical vortices open a variety of fascinating applications, ranging from femtosecond micro-nano manipulation to vortex strong-field physics. A basic requirement for these applications is that the femtosecond vortex has a clean intensity node for capturing or trapping particles. Thus far, the generation of clean femtosecond vortices remains a challenge. Here, we report on ultraclean femtosecond vortex generation by a femtosecond mode-locked laser operating in a single high-order transverse mode. By controlling the oscillation thresholds of various-order transverse modes in a laser, a pure and mode-order-tunable femtosecond Hermite-Gaussian beam is generated from the mode-locked laser and, subsequently, is converted into the femtosecond vortex by a cylindrical lens mode converter. The obtained femtosecond vortex has an unprecedented ring-to-center intensity contrast of 36 dB measured with a near wavelength-spatial-resolution detecting device, which approaches the theoretical limit of an ideal vortex beam. This Letter may open a wide range of application prospects for femtosecond vortices and motivate novel femtosecond structured beam generation directly from mode-locked lasers.
飞秒光学涡旋开启了各种引人入胜的应用，从飞秒微纳操纵到涡旋强场物理。这些应用的一个基本要求是飞秒涡旋具有一个清晰的强度节点，用于捕获或俘获粒子。到目前为止，产生清晰的飞秒涡旋仍然是一个挑战。在此，我们报道了通过工作在单一高阶横向模式的飞秒锁模激光器产生超清晰飞秒涡旋的方法。通过控制激光器中各阶横向模式的振荡阈值，从锁模激光器产生一个纯净且模式阶数可调的飞秒厄米高斯光束，随后通过柱面透镜模式转换器将其转换为飞秒涡旋。利用近波长空间分辨率检测装置测量，所获得的飞秒涡旋具有前所未有的36 dB的环心强度对比度，接近理想涡旋光束的理论极限。这封信可能为飞秒涡旋开启广泛的应用前景，并推动直接从锁模激光器产生新型飞秒结构光束。
