对于收集模式的近场光学显微镜,提出一种新的测量样品折射率和倾斜角的方法。这种方法中,使用一个反馈回路控制照射样品的光强,探针与样品保持等间距垂直振荡,照射样品的光有两束且位置对称。数字信号处理器控制照射光强改变、近场光强采样与探针振荡同步。在一个振荡周期获取一组近场光强极值,在另一个周期,改变每束光强度,隐失场分布发生改变,得到一组不同的近场光强极值,使用从多个振荡周期获取的不同近场光强极值,计算得到样品倾角,折射率。使用光栅和细胞膜对这种方法进行了测试,对光栅样品的扫描得到的形貌图显示这种方法横向分辨率优于400 nm,对细胞膜样品的测试显示细胞膜的折射率在1.4左右,从而表明这种方法不但能有效测量样品折射率,而且提供了一种使用光学信息构建样品形貌的新途径。

A new method to measure the refractive index and the inclination of the sample in collection-mode scanning near-field optical microscope is presented.In this method,the illumination intensity is controlled by a feedback loop,the vertical vibrating tip scans the sample with a constant distance and the sample is illuminated by two symmetry light beams.Altering of the illumination intensity and the sampling of the local intensity are controlled by digital signal processing to be synchronized with the vibration of the tip.A group of extreme values of the tunneling light are obtained in one oscillation period.In another oscillation period,changing of any illumination beam will modify the near field distribution.Then,another group of extreme values of the tunneling light will be obtained.The refractive index and the angle of inclination of the object can be computed from groups of extreme values that obtained from multi-oscillation periods.Grating as well as erythrocytes membrane was analyzed in our experiment.Topography images of the grating produced by our prototype instrument are shown to have a lateral resolution better than 400 nm.As for the erythrocytes membranes,the refractive index of it is about 1.4.It can be concluded that this method could not only measure samples′ refractive index effectively but also offer a new approach to rebuild samples′ topography image using optical information.