Theoretical analysis of two nodal-wedges method to enhance the vibration behavior of NSOM probe with its tip being immersed partially in liquid

In this study, a tuning fork-fiber probe system for a near-field scanning optical microscope (NSOM probe), whose fiber tip was partially dipped into liquid and vibration behavior was mechanically controlled with two nodal-wedges method, was modeled by bending vibration equations, and its resonant characteristics were numerically investigated by solving the system of equations. For the two nodal-wedges method, pin point and knife-edge balance point were newly introduced into a typical NSOM probe, and their contact positions were adjusted along the axis of the fiber probe in order to invoke versatile vibrational modes. From the numerical analysis, it was shown that the resonant frequency and the Q value of the NSOM probe were changed periodically with shifting the contact position of either the knife-edge balance point or the pin point, and that the Q value of the NSOM probe could be controlled by adjusting their contact positions as in air. Additionally, it was found that the Q value was gradually decreased with increasing the dipping depth of the fiber tip and that the Q value could be greatly enhanced at the optimal contact positions of two nodal points.