تجزیه و تحلیل حساسیت از اسکن کاوشگر میکروسکوپ نوری نزدیک میدان

In this paper, we study the dynamic modes of a scanning near-field optical microscope (SNOM) which uses an optical fiber probe; and the sensitivity of flexural and axial vibration modes for the probe were derived and the closed-form expressions were obtained. According to the analysis, as expected each mode has a different sensitivity and the first mode is the most sensitive mode of flexural and axial vibration for the SNOM probe. The sensitivities of both flexural and axial modes are greater for a material surface that is compliant with the cantilever probe. As the contact stiffness increases, the high-order vibration modes are more sensitive than the lower-order modes. Furthermore, the axial contact stiffness has a significant effect on the sensitivity of the SNOM probe, and this should be noted when designing new cantilever probes.

During the last decade the atomic force microscope (AFM) has become a very powerful and indispensable tool for studying the nature of the surface topography of diverse samples on a nanometer scale [1], [2], [3], [4] and [5]. Although AFM possesses excellent imaging capabilities, it only provides mechanical information about the material surface. To simultaneously yield the information about the mechanical and optical properties of nanometer scale surfaces, the scanning near-field optical microscope (SNOM) has been developed [6] and [7]. The SNOM usually achieves high resolutions beyond the optical diffraction limit by using an optical fiber to scan a few nanometers above the sample material surface. In a typical SNOM, the optical fiber probe is normal to the sample. The cantilever probe allows simultaneous measurement of the topography and the optical transmission of samples with high lateral resolution [8], [9] and [10]. In general, the nonlinear interaction forces occur between tip and sample surface. The dynamic responses of the cantilever probe to these surface forces include axial and flexural modes. Each mode has a different mode shape and a different sensitivity, affected by the local sample surface conditions. To obtain the highest contrast for imaging, the most sensitive modes in the system should be found and used. In this paper, the dynamic responses of the optical fiber probe of a SNOM are considered in terms of both axial and flexural vibrations. For the simple analysis, the amplitude of the surface motion is not very large, so a linearized response can be assumed. The modal sensitivities for axial and flexural vibrations are derived, and the closed form expressions are obtained.

The sensitivity of flexural and axial vibration modes for an optical fiber probe on a scanning near-field optical microscope has been analyzed. As expected, the results showed that the most sensitive mode of flexural and axial vibration for a cantilever with uniform circular cross-section is the first mode. The high-order vibration modes of the probe are more sensitive than the first mode when the sample material surface is stiffer. The sensitivity of all modes rapidly decreases when the contact stiffness increases to a high enough value. Furthermore, it can be seen that the sensitivity of axial vibration modes for an optical fiber SNOM probe can be more easily affected by contact surface stiffness than that of the flexural vibration modes.