高效产生任意矢量光场的一种方法

A method of efficiently generating arbitrary vector beams

提出一种高效产生任意矢量光场的方法.利用两个光束偏移器分别对两个正交线偏振分量进行分束与合束,将传统激光模式转化为任意矢量光场.所产生矢量光场的偏振态和相位分布通过相位型空间光调制器(SLM)加载相应的相位实时调控.由于光路系统中不涉及任何衍射光学元件和振幅分光元件,光场转换效率高,仅取决于SLM的反射率,并且光路系统结构紧凑、稳定,同轴性易于调节.实验结果显示,采用反射率为79%的相位型SLM产生矢量光场的转换效率可达到58%.

Vector beams have been used in scientific and engineering researches due to their unique focusing properties. In recent years, many methods of generating the vector beams have been proposed, among which the spatial light modulator(SLM) is widely used based on the superposition principle with using orthogonally polarized beams. However, the energy waste is generally associated with these superposition methods. How to efficiently generate vector beams is still a hot topic. Recently, we proposed an efficient method to generate tunable vector beams by using two triangular common-path interferometers(TCPIs) as the beam splitting and combining system. However, due to the complex structure of the TCPI, the system is difficult to adjust and unstable. In addition, the optical system brings about a long optical path, and the vector beams consisting of non-eigen modes will be distorted obviously with a long distance propagation. In this paper, an improved method is proposed. We replace the TCPIs with a pair of beam displacers, which act as a beam splitter and combiner, respectively. In this setup, we can arbitrarily manipulate the polarization states and phase distributions of vector beams in real time by managing the phase diagrams load on the SLM.The whole optical system does not involve any diffractive optical elements, and has a higher conversion efficiency. The improved optical system is compact and stable, and makes the adjustment of coaxiality easier.The light energy utilization depends mainly on the reflectivity of SLM. The efficiency of generating vector beams is increased to 58% by using an SLM with a reflectivity value of 79%. Several typical vector beams with phases and tunable amplitude, including cylindrical vector beams, fractional vector beams, and vector beams with double singularities, double-mode, radially variant polarization distribution, and azimuthally and radially variant polarization distribution, are generated and verified well experimentally. This method is also expected to create high-power vector beams and play an important role in laser processing and light trapping.