以寬頻種子光源做激發拉曼散射增強之研究

Abstract

拉曼光譜可以用來取得樣本的定性與定量資訊，其具有不需要樣本製備、不需要染劑標定，也不會受到水分子的影響等優點，在生醫領域上的研究越來越被重視，若此技術能夠結合具有醫學影像形貌上的判定，如光學同調斷層掃描技術，便能夠提供完整的生物樣本資訊。 本論文主要研究分為兩大方向，首先著重在皮膚中三種重要成分，包括β胡蘿蔔素、水與神經醯胺的自發拉曼散射光譜，取其斯托克散射光的部分進行光譜研究。使用低成本、具有連續波特性的雷射二極體作為泵浦光源，然而由於無可避免的會有螢光產生，因此探討各種數值去螢光方法的優劣，個別分析三樣本單獨的拉曼光譜；另外針對β胡蘿蔔素樣本，改變各實驗參數分析其訊噪比；最後取最佳的分段多項式去螢光法，並以數值方式擬合出波包成分，將三種樣本混合的拉曼結果進行分析。 受限於生物分子樣本之無序性，使得一般自發拉曼訊號強度相當微弱，因此本論文使用受激拉曼散射方法欲增強拉曼訊號。在受激拉曼散射方法中需要兩入射光源，分別為泵浦光與種子光，在泵浦光方面，使用了兩不同中心波長做兩組實驗，其為具有低成本、連續波特性的雷射二極體，中心波長為520 nm與638 nm；另外種子光源的部分，使用實驗室自產的Ce3+:YAG晶纖光纖所產生的寬頻光源，取其頻寬接近100 nm、波長由500至600 nm的寬頻特性，能夠涵蓋許多生物樣本各式各樣被泵浦光激發出的斯托克拉曼峰值，用以使訊號有所增益。目前增益並無法由實驗量測得到，因此以數值模擬方式，針對實驗實際情況做出估測僅有不到1%的增益導致難以量測，並分析泵浦光功率、種子光功率、樣本長度與拉曼增益因子對實驗結果的影響與改善，並預測以460-nm LD泵浦光激發β胡蘿蔔素樣本，可使拉曼增益超過10倍之量值。

Raman spectroscopy can be used to obtain the qualitative and quantitative information of samples. And the Raman measurement has the advantages that it does not need samples preparation, no need for staining, and it would not suffer from the impact of water, etc. In the field of biomedical research, Raman spectroscopy increasingly gets more attentions. If this technology can be combined with a 3D medical imaging technology, for instance, optical coherence tomography, more complete information of the biological samples can be obtained. In this thesis, it is divided into two directions. First of all, we will focus on three important ingredients in the human skin, including β-carotene, water, and ceramide. The Stokes scattering of the spontaneous Raman scattering spectra of these three samples were obtained to study. We use a low cost and continuous-wave laser diode as the pump light source. Because the spectra will inevitably be mixed with fluorescence produced by samples, we tried several methods, and discuss their pros and cons to eliminate the fluorescence. Then choose β-carotene to be the object to analyze the impacts of the results from calculating the signal to noise ratio when changing the experimental parameters. And finally, make use of the best method to eliminate the fluorescence that we have discussed on the Raman spectra of three mixed samples. And numerically fit the wave packet to several Raman peaks. Due to the amorphous nature of biomolecule samples, the spontaneous Raman signal strength generally is quite weak. So this thesis uses stimulated Raman scattering method to enhance the Raman signals. The stimulated Raman scattering method requires two incident light source including the pump and the seed. About the pump light, we use two kinds of laser diodes, which is low cost and continuous-wave and with different center wavelengths, to get two sets of data. The center wavelengths of the laser diodes are 520 nm and 638 nm. About the seed light, we use a laboratory-grown Ce3+:YAG crystal fiber to produce a broadband light source, which bandwidth is approaching 100 nm and the wavelength range is from 500 to 600 nm. It can cover a wide range of Stokes of Raman spectra which is provided by biological samples that pumped by laser diode in order to enhance the signals. Currently, we could not measure the enhancement from our experiments. Therefore, we use a numerical simulation to estimate the actual situation of our experiments to get the enhanced value that is less than 1% no wonder it is difficult to measure. Then we change the parameters include pump power, seed power, sample length and Raman gain factor to analyze the influences to the results and predict the better choice of parameters if we want to measure the enhancement easily in the future.