利用飞秒脉冲诱导生成的具有渐变折射率分布的等离子体通道产生空心光束.当飞秒脉冲在非线性介质中传输时将电离产生等离子体通道, 该等离子体通道具有渐变的折射率分布, 等离子体通道中激光束只能在电子密度低于临界等离子体密度的区域传播, 故当探测光束在等离子体通道边缘传输时将偏转形成空心光束.当泵浦光束功率为8 mW时, 探测光束转变为典型的空心光束结构；当泵浦光束的入射功率、重复率或等离子体通道中轴向电子密度改变时, 等离子体通道中可供探测光束通过的区域将随之发生改变, 这将导致空心光束中黑斑的面积发生变化.因此通过调节泵浦光束的入射功率和重复率可以控制产生空心光束的黑斑大小.

The generation of hollow beams were demonstrated by using a plasma channel induced by pump pulses. A plasma channel will be generated as femtosecond pulses propagating in the nonlinear media, the distribution of refractive index in the plasma channel induced by pump beams is similar to a graded-index lens, besides, laser beams can only propagate in the plasma if the electron density of the plasma is less than the critical value, the probe beam is refracted and transformed into a hollow beam when it passes through in the periphery of the plasma channel. It finds that the probe beam begins to transform into a characteristic hollow beam structure when the power is 8 mW. When the power or repetition rate of the pump beam and the electron density in the plasma channel are changed, the region of the plasma where the probe beam can pass through is also changed, resulting in a controllable dark spot of the hollow beam.