Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
Anal Chem. 2011 Dec 15;83(24):9438-42. doi: 10.1021/ac2021008. Epub 2011 Nov 22.
A pulsed (4.4 ns pulse length) frequency-doubled Nd:YAG laser operated at 10 Hz was used to generate Raman scattering of samples at a distance of 12 m. The scattered light was collected by a 6 in. telescope, and the Raman spectrum was recorded using an Acton SP-2750 spectrograph coupled to a gated intensified charge-coupled device (ICCD) detector. Applying a spatial offset between the point where the laser hit the sample and the focus of the telescope on the sample enabled collection of Raman photons that were predominantly generated inside the sample and not from its surface. This is especially effective when the content of concealed objects should be analyzed. High-quality Raman spectra could be recorded, within 10 s of data acquisition, from a solid (NaClO(3)) as well as a liquid (isopropyl alcohol) placed inside a 1.5 mm thick opaque low-density polyethylene (LDPE) plastic bottle. The applied spatial offset was also advantageous in cases where the surface of the container was highly fluorescent. In such a situation, Raman spectra of the sample could not be recorded when the sampling volume (telescope observation field) coincided with the focus of the excitation laser. However, with the use of a spatial offset of some millimeters, a clear Raman spectrum of the content (isopropyl alcohol) in a strongly fluorescent plastic container was obtained.
采用脉宽为 4.4ns 的倍频 Nd:YAG 激光器，工作频率为 10Hz，在 12m 距离处产生样品的拉曼散射。散射光由 6 英寸望远镜收集，并用耦合至门控增强型电荷耦合器件（ICCD）探测器的 Acton SP-2750 光谱仪记录拉曼光谱。在激光照射样品的点和望远镜在样品上的焦点之间施加空间偏移，从而可以收集主要在样品内部而不是从其表面产生的拉曼光子。当需要分析隐藏物体的含量时，这一点尤其有效。可以在 10 秒的数据采集内从置于 1.5 毫米厚不透明低密度聚乙烯（LDPE）塑料瓶内的固体（NaClO(3)）和液体（异丙醇）中记录高质量的拉曼光谱。所施加的空间偏移在容器表面高度荧光的情况下也很有优势。在这种情况下，当采样体积（望远镜观察场）与激发激光的焦点重合时，无法记录样品的拉曼光谱。但是，通过使用几毫米的空间偏移，可以获得强荧光塑料容器中内容物（异丙醇）的清晰拉曼光谱。
