空心光束尺寸的精确调控

Precise controll of hollow beam size

提出一种利用环缝精确调控空心光束尺寸的新方法.首先用环缝和旋转毛玻璃产生非相干准单色的环形光源,再经过薄透镜聚焦后产生空间相干度按第一类零阶贝塞尔函数分布的贝塞尔-谢尔模型光场,最后通过轴棱锥对贝塞尔-谢尔模型光场的线聚焦,产生空心光束.通过改变环缝大小控制非相干环形光源尺寸,对贝塞尔-谢尔模型光场的空间相干度分布进行调制,从而精确控制空心光束尺寸.应用广义衍射积分理论以及贝塞尔-谢尔模型描述该光学系统所产生的光场分布.设计相关实验进行验证,理论分析、数值模拟与实验结果相符合.该研究成果对不同尺寸粒子的微操控提供有力的手段.

A novel technique to generate precisely size-controlled hollow beams by controlling the diameter of circular slit is proposed.Firstly,a laser beam is transformed into a quasi-monochromatic incoherent annular source by a rotating ground-glass disk and circular slit.Then,after passing through a thin converging lens,a J0-correlated Schell-model beam is synthesized by placing the annular incoherent source in the first focal plane of the thin lens.Finally,a partially coherent hollow beam is generated by focusing the J0-correlated Schell-model beam with an axicon.Based on the diffraction theory and the propagation law of partially coherent beams,the cross-spectral density function is derived to calculate the intensity distribution of the cross section and the radial intensity distribution along the propagation axis behind the axicon.By carrying out the theoretical calculation,the proposed optical system generates a partially hollow beam,and the size of the hollow beam expands continuously as the propagation distance increases.Before further investigating the effect of the diameter of incoherent annular source on the hollow beam behind the axicon,we also calculate the intensity distribution of the cross section and the size of hollow beams along the propagation axis at z=70 mm with the source diameters being 1,2,3,4 and 5 mm,respectively.Results show that the size of the hollow beam also increases with the diameter of incoherent annular source increasing.In this case,the size of the hollow beam can be precisely controlled by tuning the diameter of incoherent annular source through circular slit.We also design and conduct an experimental generation of the hollow beam and investigate the propagation properties.In the experiment,we control the diameter of the annular source by tuning the diameter of the circular slit located before the rotating ground-glass disk.And the diameter of the annular source is equal to that of the circular slits.When the sizes of circular slits are 1,2,3,4 and 5 mm,respectively,the corresponding hollow beams are measured by CCD.Experimental results show that the size of hollow beam can be controlled by the propagation distance and the diameter of the circular slit.The intensity profiles are in good agreement with theoretical predictions.Therefore,the size of hollow beams can be precisely generated and controlled by the proposed system so that the optical system can be flexibly employed in optical trapping and manipulation of particles with different sizes.The results may provide a powerful tool for manipulating the micro- and nano-particles.