空间偏移拉曼光谱技术及数据处理方法研究

Research on Spatial Offset Raman Spectroscopy and Data Processing Method

传统拉曼光谱分析技术在对容器内未知样品进行检测时极易受到容器壁的荧光和拉曼散射干扰,其商业应用往往仅限于透明塑料或玻璃包装的情况。由于光子在介质内部的迁移方向具有随机性,与表层相比内部深层处产生的拉曼散射光子在扩散过程中更易于横向迁移,因此偏离激光入射点不同距离的拉曼光谱包含了不同深度层的拉曼光谱信息。空间偏移拉曼光谱技术通过将拉曼光收集点偏离激光入射点,能够抑制容器壁的荧光和拉曼散射干扰,从而实现对有色、不透明包装内样品的有效检测。通过设计搭建了空间偏移拉曼光谱实验装置,实现-1.0~10.0 mm偏移距离的可调节。使用青色、不透明的1 mm厚PMMA平板来模拟容器壁,使用碳酸钙(CaCO3)粉末作为内部待测样品。分别采用传统方式(零偏移)和空间偏移方式对容器内样品进行测量。对采集的原始光谱首先进行平均和7阶多项式拟合去除基线(荧光),然后以3个最大特征峰的平均值作为光谱强度的评价指标,对空间偏移拉曼光谱信号随偏移距离的变化规律进行分析,发现:随着空间偏移距离的增大,容器壁的拉曼散射强度快速下降,而内部样品的拉曼散射强度先上升后缓慢下降;对于均匀厚度、各向同性的样品,变化趋势关于零偏移两侧对称,此外光束的斜入射会引起轻微的不对称;在某个偏移距离处样品与容器壁的光谱强度比值达到最大值,存在最优探测偏移距离,对于此次样品其最优偏移距离为1.2 mm。在容器和样品材质未知的情况下,采用比例相减的方法仍可以得到各层干净的拉曼光谱,通过对零偏移和最优偏移处的光谱进行计算,分别得到容器壁和内部样品干净的拉曼光谱,实现对内部样品的有效检测。研究结果在一定程度上证明了空间偏移拉曼光谱技术在不透明、有色容器内样品的检测方面的潜力,为进一步研究空间偏移拉曼光谱技术及数据处理方法提供基础。

Traditional Raman spectroscopy is highly susceptible to fluorescence and Raman scattering of the container wall when detecting unknown samples in containers, which often limits its commercial applications to transparent plastic or glass packaging. Since the photon migration direction inside the medium is random, the Raman scattered photons generated at the inner deep layer are more likely to migrate laterally during the diffusion process. Therefore, the Raman spectrum at different distances from the laser incident point contains different Raman spectral information of depth layers. The spatially offset Raman spectroscopy(SORS) can suppress the fluorescence and Raman scattering interference of the container wall by deviating the Raman light collection point from the laser incident point, there by realizing effective detection of the sample in the colored and opaque package. By designing a SORS experimental device, the offset distance of-1.0~10.0 mm can be adjusted. A cyan, opaque 1 mm thick PMMA plate was used to simulate the container wall, and calcium carbonate(CaCO3) powder was used as the internal sample to be tested. The samples were measured by the conventional method(zero offset) and the spatially offset method. The acquired raw spectra were first averaged and fitted by a 7 th order polynomial to remove the baseline. Then the average of the three largest spectral peaks was used as the spectral intensity, and the variation law of the SORS signal with the offset distance was analyzed. It was found that: as the spatial offset distance increases, the Raman scattering intensity of the container wall decreases rapidly, while the Raman scattering intensity of the internal sample first rises and then decreases slowly;for samples of uniform thickness and isotropic, the trend of change is symmetrical about the zero offset, and the oblique incidence of the laser beam causes a slight asymmetry;at a certain offset distance, the ratio of the spectral intensity of the sample to the container wall reaches a maximum value, and there is an optimal detection offset distance(for this sample, the optimal offset distance is 1.2 mm). In the case where the material of the container and the sample is unknown, the clean Raman spectrum of each layer can still be obtained by the method of proportional subtraction. By calculating the spectrum at the zero offset and the optimal offset, the clean Raman spectra of the container wall and the internal sample are obtained respectively, which can be used in later spectral analysis and identification processes. This work demonstrates the potential of SORS for the detection of samples in opaque, colored containers, and provides a basis for further research on SORS and data processing methods.