本研究期望在暗場架設下量測粒子的拉曼訊號，因為在暗場的架設下來自背景基板的散射訊號被物鏡接收到的比例大幅減少，而基板上粒子的散射訊號相對地就比較明顯，所以在暗場下觀察影像時可以發現目標粒子與基板的對比度比較好，因此如果可以在暗場架設下量測到拉曼光譜，預期可以得到跟觀察影像時相同的結果；在本研究中，使用氦氖雷射作為激發光源量測拉曼訊號，氦氖雷射的光強度分佈是高斯分布，雷射光束的縱截面是一個圓點，而能量集中在光束的中心，如果直接入射到暗場顯微鏡系統中，雷射光束大部分的能量會被暗場環(dark field annular aperture)擋住，因此本研究提出的方法是使用兩片相同規格錐形鏡(Axicon)對雷射光束進行光束整形，調整兩片Axicon鏡片的擺放位置，利用兩片Axicon產生圓弧型光束，雷射光束的光強度都集中在圓弧上，使圓弧型光束通過暗場環在暗場的架設下觀察影像以及量測拉曼訊號；本研究討論了使用兩片Axicon所嘗試過的架設，也整理了如何產生圓弧型光束的光學架設以及架設方法，並配置樣品使用矽(silicon)作為基板，在基板上灑上大小為1 um的聚苯乙烯(polystyrene, PS)粒子作為本研究的量測樣品，使用圓弧型雷射光束作為光源在暗場下量測矽基板與單顆PS粒子的拉曼訊號，觀察兩者之間的拉曼訊號強度比例，並與傳統的拉曼訊號量測方式所量測到的拉曼光譜作數據比較，實驗結果發現暗場下量測到的拉曼光譜，基板與粒子的拉曼訊號的對比度有明顯的提升。

We attempt to measure the Raman signals of a single particle through the setup of darkfield microscopy. The darkfield microscopy setup has an annular aperture, which can block central region of the incident light and create an annular beam. In this setup, the annular beam can illuminate the specimen obliquely. At an oblique angle illuminating specimen can reduce the scattering signals of the substrate collected by the objective, but the scattering signals of the specimen are still captured by the objective. In the darkfield setup, the scattering signal intensity ratio between the substrate and specimen will be closer. In order to measure the Raman signals, the He-Ne laser, whose intensity distribution is Gaussian, is used as the illumination light source, so the intensity of the laser beam will be blocked by the annular aperture in the darkfield setup. To overcome this problem, Axicon, an optical lens with a conical surface, is used to transform the shape of the Gaussian beam into a crescent shaped beam. The crescent shaped beam can pass through the annular aperture and reduce the loss of the intensity. The crescent shaped beam is used as the illuminating light source in the darkfield setup to measure the Raman signal of a single polystyrene (PS) particle on the silicon substrate. We expect the Raman signals from the silicon substrate will be reduce in darkfield setup, so the Raman signal intensity ratio between the particle and the substrate will be closer.

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