电磁诱导透明效应增强的四波混频光谱技术用于锂同位素高分辨痕量测量

Lithium (Li) isotopic ratio method has an important application in the study of Earth & Environmental Science, such as surface weathering investigation, etc. Nowdyas, mass-spectroscopy is the main method used in Li isotope measurement. However, the sample pretreatment processe of this method is quite complicated and time-consuming, including separation, purification and enrichment processes. These processes can cause sample waste, analysis speed slow and efficiency low, etc. The sample pretreatment process of spectrometry is simple. But the current spectroscopic techniques cannot distinguish the Li-7 D1 line and Li - 6 D2 line effectively. In view of this, we propose to measure Li isotopes by electromagnetically induced transparency (EIT) enhanced four-wave mixing (FWM) spectrometry and study the relevant physics problems: invstigating enhancement mechanism of EIT on FWM signal intensity, deducing the relationship between the content of Li isotopes in the analytes and FWM signal intensity, studying on the influence factors of the relationship according to the experiment, measuring the Li isotopes contents in the earth and environmental samples (rock, soil and water, etc) and providing a quantitative basis for the study of earth and environmental science. There are two main advantages of this technique. One is high resolution. It is a Doppler-free method and can avoid the interference between Li-7 and Li-6. The other one is high sensitivity. So it does not need a sample enrichment process. This project is to explore a new method for the study of Earth & Environmental Science.

锂(Li)同位素比值法在地表风化等地球环境科学研究中有着重要的应用。质谱法是目前Li同位素测量的主要手段，但这种方法的样品预处理过程（分离、提纯、富集）复杂，会造成样品浪费、分析速度慢、效率低等。光谱法的样品预处理过程简单，但目前的光谱技术不能有效分辨Li-7的D1线和Li-6的D2线。鉴于此，本项目提出利用电磁诱导透明效应（EIT）增强的四波混频（FWM）光谱技术来测量Li同位素并研究相关的物理问题：研究EIT效应对FWM信号的增强机制；理论推导FWM信号强度与样品浓度之间的量化关系，结合实验研究影响该量化关系的因素；实现地球环境样品（岩石、土壤、水体等）中的Li同位素的高精度测量，为地表风化研究提供定量的依据。该技术的优势在于：分辨率高，可消除多普勒展宽，且能避免Li-7对Li-6的干扰；灵敏度高，无需样品富集过程。为此，本项目的开展将为地球环境科学领域提供一种新的研究手段。

锂(Li)同位素比值法在地表风化等地球环境科学研究中有着重要的应用。质谱法作为目前 Li 同位素测量的主要手段，虽然分析准确、耗样量小，但样品预处理过程（分离、提纯、富集）复杂，会造成样品浪费、分析速度慢、效率低等。光谱法的样品预处理过程简单，但由于多普勒展宽的存在，无法将 7Li的 D1 线和 6Li 的 D2 线分开。鉴于此，本项目基于四波混频（FWM）光谱技术来测量 Li 同位素并研究相关的物理问题：从理论和实验上研究了样品浓度、入射功率等因素对于FWM信号强度的影响，测量了Li的标准溶液的同位素比值，为了验证结果，原子吸收光谱（AAS）同样被用来测量Li同位素比值，结果表明两种方法所测结果近似，证明的FWM的正确性与可靠性。接下来，我们将该方法成功用于岩石样品中Li同位素的测量，为地表风化研究提供定量的依据。但由于实际样品中光学均匀性较差，严重的光散射造成了信号强度大幅度下降，针对该问题，我们采用贝塞尔光束的自愈特性增强了FWM的信号强度。该技术的优势在于：分辨率高，可消除多普勒展宽，灵敏度高，无需样品富集过程，为地球环境科学领域提供一种新的研究手段。此外，我们还分别研究了基于自相位调制、交叉相位调制的贝塞尔光束的产生，尤其是后者，它具有装置简单，成本低，损伤阈值高的特点，更重要的是获得的贝塞尔光束尺寸可控。我们也将产生的贝塞尔光束应用到微粒的捕获与操控，该部分的工作在原子引导、激光捕获、激光加工、光学成像、非线性光学过程增强等方面都有着显著的意义。