中文摘要：

数值计算了局域椭圆偏振光束强聚焦时在焦平面上的横向场强分布、纵向场强分布、横向能流以及纵向角动量分布.结果显示在焦平面上光束总的纵向角动量为零,但在不同象限光束具有不同方向的纵向角动量.当相位延迟角度在0到π之间变化时横向场强分布基本不变,但纵向场强分布有很明显的变化.液晶相位延迟器由外部电压控制,使其相位延迟角度能在0到π之间可以连续取值.因而液晶相位延迟器的外接电压可以实现对焦平面上的纵向场强以及纵向角动量的实时调控.

英文摘要：

When a radially-polarized beam passes through a wave plate,the polarization distribution of the beam strongly depends on the retardation angle and the spatial position. When the retardation angle is changed from 0 to π,the polarization of the beam becomes the local elliptic polarization with non-uniform polarization distribution. The rotating direction of polarization in the first and third quadrants is opposite to that in the second and fourth quadrants. In this paper we have numerically simulated the transverse and longitudinal electric field intensity,the transverse energy flux and the longitudinal angular momentum of the tightly focused beam in the focal plane. Our results show that the sum of the longitudinal angular momentum in the focal plane is zero,but it is varying in different quadrants. The liquid crystal variable retarder （LCVR） is adopted as a real-time continuous tunable wave plate with its retardation angle δ changing from 0 to π by varying the applied voltage. In this case the phase retardation angle δ introduced by the LCVR can be used as a control over the longitudinal electric field intensity and the longitudinal angular momentum.