产生纳米级暗中空光束的方法研究

用时域有限差分法，给出光纤头近场区电场强度模的空间分布.讨论了当光纤纤芯分别取不同尺寸时，对此空间光场强度的影响.要想得到较大范围的暗中空光束，必须增加光纤纤芯尺寸.并且，对光纤纤芯尺寸取一较大值和光纤中空区域尺寸取一较小值时的情况进行讨论，可得在光纤头附近可以出现与光纤中空区域尺寸大小相当的暗斑(10¹ nm量级).但是，暗中空光束中背景光较强.为此，将光纤的空心设计为金属. 发现此时中心暗斑的背景光明显减弱，在近场区域可获得较为理想的暗中空光束.如进一步缩小光纤中空区域尺寸，可以在光纤头附近获得暗斑更小甚至纳米量级的暗中空光束.为获得一种纳米量级的暗中空光束提供一种方法.

A method of acquiring a dark hollow beam of nanometer level

By using the finite difference time-domain (FDTD) method, the distribution of the modulus of the electric field intensity is obtained in the near field of an optical fiber head.We found that different dimensions of the cylindrical core in a hollow optical fiber had an influence on the electric field intensity. It is concluded that the size of the cylindrical core must be increased to make the hollow beam to cover a larger area. At the same time, after discussing the two situations that the size of the hollow optical fiber either rather large or rather small, we obtained a dark spot in the near field of the fiber that was almost of the same size as the hollow region (10 nanometer level). However, the background light in the dark hollow beam was brighter, and so the hollow region was designed to be a metal (such as silver). We found that the background light in the dark spot became evidently weaker and a cleaner dark hollow beam was acquired in the near field. When the hollow region was made smaller, the dark spot in the near field would become smaller, even reaching the nanometer level, which offered a method of obtaining a dark hollow beam of nanometer level.