Research On Some Key Problems In Scanning Near-field Optical Microscopy

With the help of scanning probe technique applied in optical field, the super high-resolution images beyond the diffraction limit can be obtained with the Scanning Near-field Optical Microscopy(SNOM). In the past decades the lateral and the stability of SNOM has been advanced greatly than before. Though the resolution of which is still lower than Scanning Tunneling Microscopy(STM) and Atomic Force Microscopy(AFM), SNOM has its own advantage to obtain the optical contrast information of the sample. In this thesis the disadvantage of traditional SNOM such as the nonlinearity and the slower scanning speed are discussed and a new set of the modular SNOM with a pair of DSP control system is built; A module of scan head with collecting real timely nonlinearity data is developed and the arithmetic of the scanning nonlinearity correcting is build up; A quartz pitch-optical fiber resonator probe to improve the scanning speed of SNOM and a new type scanner with four piezoelectric tubes are designed and experimented.The main research contents of this thesis are listed as follows:1. A new set of SNOM using DSP controlling system is built up. There are several modules:the main DSP controlling system, the feedback DSP system which control the tip-sample distance, the phase detecting system which supply the feedback signal to the feedback DSP system, and so on. The XY scan control arithmetic and PID control arithmetic are developed.2. The exsistence of nonlinearity in the scanner of SNOM is analysed. Image post-processing software for the correction of scanning nonlinearity is developed. A scanner with a PSD which can get the tip's position in real-time is designed and experimented. The quadratic polynomial model and the BP model of Neural-Net Algorithms are introduced to process the scanner nonlinearity data and to get the modle of linearity correction.3. A new module of the quartz pitch-optical fiber probe is advanced which has higher scanning speeds than the module of the tuning fork-optical fiber probe. The response speed of tip-sample distance change using the phase regulation is more quickly than that with the amplitude.4. A new scanner based on four piezoelectric tubes connected with spring hinge and sample stage is designed. The FEM software of ANSYS is used to analyse the mechanics behavior of the scanner:The XYZ scanning ranges of this new scanner are all bigger in three dimension; This new scanner's static and dynamic properties simulation with the finite element method has carried, and its pre-experiment has accomplished.