离轴拉盖尔-高斯涡旋光束传输中的光斑演变

在产生涡旋光束过程中, 固体激光器所输出的光束中心 很难与螺旋相位板的中心完全对准, 实际出射的光束为离轴涡旋光束. 在衍射理论的基础上, 对离轴涡旋光束的传输进行了研究, 推导了离轴涡旋光束传输一段距离后电场和光强的解析表达式.研究表明, 与理想的涡旋光束不同, 离轴涡旋光束具有非对称性的光强分布, 在传输过程中光斑除了展宽外, 涡旋暗核还会发生移动. 拓扑电荷数的大小只影响到光束的展宽, 拓扑电荷数为正时, 暗核沿着逆时针切线方向移动; 拓扑电荷数为负时, 暗核沿着顺时针的切线方向移动, 该结果对长距离探测涡旋光束的对准问题起到指导作用.

Change of the off-center Laguerre-Gaussian vortex beam while propagation

The center of the Gaussian beam from solid laser cannot be completely aligned with the center of the spiral phase panel (SPP) while vortex beam is produced by SPP. The projecting beam from the SPP is actually an off-center vortex beam. Based on the diffraction theory, the propagation of off-center vortex beam is investigated. The analytic expressions of the electric field and the intensity are derived in the observation plane while the beam propagates a certain distance. It is shown that the intensity distribution of the beam changes asymmetricly. Besides the spreading, the core of the vortex beam moves while propagating, which is quite different from that of the ideal vortex beam. The magnitude of topological charge determines the spreading of the beam and has no influence on the motion of the vortex core. Furthermore, the sign of the topological charge determines the direction along which the core moves. If the topological charge is positive, the core will move in the tangential direction anticlockwise; if it is negative, the core will move in the tangential direction clockwise, from which the conclusion can provide a guidance for the beam aligning while the vortex beam is detected under the condition of long distance propagation.