| Summary: | 碩士 === 國立成功大學 === 工程科學系碩博士班 === 97 === The optical spatial resolution of conventional aperture near-field scanning optical microscopy is limited by cut-off effect and thermal noise effects. An apertureless near-field scanning optical microscope (aNSOM) has been developed to break the limitation. The localized electromagnetic field near the region between the sample and the tapping tip of atomic force microscopy (AFM), and then the effective scattering field which including near-field optical signal will be detected by far-field microscopy. This thesis attempts to develop an aNSOM based on a commercial AFM to achieve an optical spatial resolution better than 10 nm. Furthermore, the aNSOM is applied to measure near-field fluorescence signal
In the system, the modulated optical signal including the near-field signal and background noise is collected by a far-field microscope. In order to improve the near-field image with a high signal-to-noise ratio (SNR), the signal from the tapping tip at high harmonic terms is demodulated for both homodyne and heterodyne interferometric detections. With the help of an addition reference signal, the heterodyne detection can improve the SNR by rejecting near-field background noise. To test the system performance, a near-field fluorescent image from fluorescence molecules is grabbed. The interaction between the fluorescence signal and the tip is studied to assist how to obtain the fluorescent signal more efficiency. Eventually, the system could play a key role in biomolecular field, and provide fluorescence image with a molecular -scale resolution.
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