由於傳統的光學顯微鏡會受限於光學的繞射極限(diffraction limit)，其軸向與側向解析度均無法達到小於波長一半的空間解析度；為了突破此光學繞射的極限，發展了孔徑式近場掃描式光學顯微鏡(near-field scanning optical microscopy，NSOM)，但受到截止效應、熱傷害等問題影響，其空間解析度仍然侷限在50nm左右。為了達到更佳的空間解析度，我們實驗室已研發以一般商用的原子力顯微鏡(atomic force microscope，AFM)為基礎，並配合不同照射與偵測的光學及機械系統設計、資訊擷取卡為系統控制的核心，建立一無孔徑近場掃描式光學顯微鏡(apertureless near-field scanning optical microscopy，aNSOM)。本論文主要目的為改善此aNSOM系統，提高其光訊號的訊躁比(signal-to-noise ratio，SNR)，達到同時偵測樣品之形貌、近場強度及相位等高空間解析度的影像。
於光學訊號處理與擷取上，主要是以不同方式的聚焦光照射於原子力顯微鏡之探針針尖上，並以雪崩二極體(avalanche photodiode，APD)為遠場偵測器，偵測針尖與樣本表面的交互作用後產生之散射場中包含了微弱近場光學訊號及強大的遠場背景雜訊。為了從背景雜訊中擷取近場光學訊號，使用針尖敲打頻率的高階振盪頻率作解調變，並搭配內差式(homodyne)及外差式(heterodyne)的干涉術以得到近場光學訊號。另外，於系統機構的測試中，以整體系統精準調整為前題下作了不同的測量，從探針振盪情形、探針選擇、聚焦光打到探針上的調整校正、干涉條件的校正以及內差式干涉術與外差式干涉術的比較等分析後，得到真正的近場光學訊號所需要的各項調整校正，並使其應用於具表面電漿子(surface plasmons)特性結構的量測。

The axial and lateral spatial resolutions of conventional optical microscopy are restricted by optical diffraction limit. In order to break the diffraction limit, a near-field scanning optical microscope (NSOM) has been successfully developed; however, the lateral spatial resolution is still limited to 50 nm due to light throughput and thermal heating. To improve the current resolution, an apertureless near-field scanning optical microscope (aNSOM) based on a commercial atomic force microscope (AFM) combined with optical, mechanical, and electrical system designs at different illuminations and detections was preliminarily developed in our lab. In this thesis, the aNSOM system is improved to increase the signal-to-noise radio of optical signal, and then topography, optical intensity and phase images with higher spatial resolutions can be detected simultaneously.
In optical signal processing and detection, the optical signal is collected by high frequency response avalanche photodiodes (APDs) by adjusting the optical signal collection at different illuminations on the AFM tip apex. The collected scattering signal mainly includes the weakly near-field optical signal of tip-sample interaction and large unwanted background noise signal. To eliminate the unwanted background signal and enhance the near-field signal, the demodulation technique of high-order harmonics of tip tapping frequency is adopted at homodyne and heterodyne interferometry, respectively. Moreover, tip tapping and selectivity, opto-mechanical alignment, interferometric alignment, and homodyne and heterodyne detections are considered and adjusted to improve the aNSOM. Currently, a better near-field optical signal is achieved, and then the aNSOM system is utilized to measure the near-field signal of surface plasmonic structures.

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