On the basis of the stationary phase principle, we construct a family of shaping nondiffracting structured caustic beams with the desired morphology. First, the analytical formula of a nondiffracting astroid caustic is derived theoretically using the stationary phase method. Then, several types of typical desired caustics with different shapes are numerically simulated using the obtained formulas. Hence, the key optical structure and propagation characteristics of nondiffracting caustic beams are investigated. Finally, a designed phase plate and an axicon are used to generate the target light field. The experimental results confirm the theoretical prediction. Compared with the classical method, the introduced method for generating nondiffracting caustic beams is high in light-energy utilization; hence, it is expected to be applied conveniently to scientific experiments.

无衍射光束是一种能在自由空间稳定传输的光束。近来，一类具有复杂光学形态的无衍射光束被引入，比如马蒂厄光束、抛物光束、非对称贝塞尔光束等。为了产生具有复杂结构的无衍射光束，需要对光波进行复振幅调制，即同时调制光波的振幅和相位。但目前的商用光学调制元件只能调制光波的振幅或相位。本文基于二元计算全息法，编码二维复透过率函数分布，构建了具有复振幅调制功能的二元实振幅非负计算全息图。利用实验室自主研发的投影成像光刻系统，对银盐干板进行曝光处理，经显影、定影处理，将其加工为相应的振幅掩模板，用来产生精确的具有复杂结构的无衍射光束。以无衍射马蒂厄光束为例，采用罗曼型迂回相位编码方法，在全息图每个抽样单元内开一个矩形通光孔径，通过改变通光孔径的面积来对复值光波的振幅进行编码，通过改变通光孔径中心偏离抽样单元中心的距离，来对复值光波的相位进行编码。最终构建了两种产生马蒂厄光束的典型二元实振幅计算全息图，其像素数高达28000 pixel×28000 pixel。之后利用加工好的振幅掩模板，准确、方便、高效地产生了的椭圆系数q=10，拓扑荷数m=0与m=1的第一种偶型马蒂厄光束，其他类型的马蒂厄光束可相应产生，这是一种光束形态多样、光束结构复杂的无衍射光束。实验结果证实，采用罗曼型迂回相位编码方法产生具有复杂结构的无衍射光束，有效避免了实验过程中分离的相位调制元件和振幅调制元件之间的对准误差，二元计算全息编码法是一种能用来调控产生复杂结构无衍射光束的新途径。