The Study of Raman Scattering Enhancement by Broadband Light Source
Date Issued
2015
Date
2015
Author(s)
Jiang, Wan-Lin
Abstract
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.
Subjects
Raman spectroscopy
spontaneous Raman scattering
stimulated Raman scattering
Stokes
cerium-doped yttrium aluminum garnet
β-carotene
water
ceramide
Type
thesis
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