为了研究扫描近场光学显微镜(SNOM)光纤探针的光学特性, 采用基于场追迹方法的光学软件VirtualLab Fusion进行了仿真实验, 取得了SNOM光学探针尖端外部光场的分布情况。结果表明, 沿z轴方向, 不同截面上的光场分布都会呈现小孔衍射的图案, 其中心斑点中心强度随着z值的变大而呈近似指数函数衰减, 到z=100nm位置处几乎衰减为0; 中心斑点轮廓线的半峰全宽随着z值的变大而呈现先不变后增大的趋势, 其拐点处于z=20nm位置处, 此时对应的中心强度值为7.2V/m2,这个强度值按指数函数计算正好处于z=0nm位置处强度的e-2。结果清晰显示了SNOM光学探针的光学特性, 证实SNOM探针工作时需要与样品表面保持在10nm左右的必要性。

In order to study optical properties of an optical fiber probe in scanning near-field optical microscopy (SNOM), simulation experiment was carried out by using the optical software VirtualLab Fusion based on field tracing method. The distribution of external optical field at the tip of SNOM optical probe was obtained. The results show along z axis, the distributions of optical field on different sections show the pattern of small aperture diffraction, the center intensity of center sample decreases exponentially with the increase of z value, and is almost attenuated to 0 at the position of z=100nm. With the increase of z value, full width at half maximum of center speckle contour remains stable at first and then increases. Its inflection point is at the position of z=20nm. The corresponding center strength value is 7.2V/m2 at this point. If calculated by the exponential function, this strength is at exactly e-2 of the position of z=0nm. The study shows the optical properties of SNOM optical probe. It confirms that it is necessary for SNOM probe to keep the distance of around 10nm from the sample surface.