利用拉曼光譜靈敏偵測水中化學物質

Abstract

我們利用一個波長為532nm、平均能量為5mW的脈衝式被動式Q開關(Passive Q Switch microchip Laser)微晶片雷射，量測不同濃度甲醇(methanol)水溶液中的拉曼訊號。為了增進偵測極限，我們利用液體波導管增加液體之拉曼訊號強度，同時降低光電倍增管的熱效應雜訊。本論文的目標是研發一套脈衝式微晶片雷射的拉曼光譜偵測系統，用以分析甲醇水溶液的濃度，並量測甲醇最低濃度的偵測極限。由於使用脈衝式雷射，拉曼訊號也是脈衝式，因此我們以雷射本身訊號做觸發，利用boxcar積分器截取訊號。在使用石英柱當樣品槽時，我們可以量測到濃度為5%的甲醇訊號，而使用液體波導管時，可以量測到濃度為0.5%的甲醇訊號。 如果使用較大功率的微晶片雷射，相信還可以降低甲醇最低濃度的偵測極限。由於小功率的微晶片雷射非常輕便並可攜帶，本實驗發展的拉曼光譜偵測系統可望用在即時全天候的河川環境監測上。

Utilizing Raman spectroscopy technique, we use a 532-nm, 5-mW average power, passive Q-switch microchip laser to measure aqueous methanol of different concentrations. In order to lower the detection limit, we use a liquid waveguide to enhance the liquid Raman signal and a cooling system to reduce the thermal noise from photomultiplier tube (PMT). The goal of this dissertation is to construct a Raman spectroscopy system utilizing the pulsed microchip laser and to analyze the detection limit of the system in terms of the concentration methanol. In this experiment, a boxcar integrator system is used to grab the pulsed Raman signal triggering by the laser source. The measured detection limit of methanol concentration are 5% by using quartz cell and 0.5% by using liquid waveguide, separately. It is believed that the detection limit of aqueous concentration could be further reduced if we use a higher power microchip laser. With the advantages of compactness and portability, we hope this system to be used in real time monitoring the pollution of rivers.