Na_2SO_4溶液激光拉曼/激光诱导击穿光谱联合探测

Joint Analyses of Na_2SO_4 Solution by Laser Induced Breakdown Spectroscopy and Raman Spectroscopy

光谱技术应用于海底极端环境下多参数、多相态、无接触探测已成为深海化学传感器发展的一个重要方向,尤其是水下激光拉曼光谱技术和水下激光诱导击穿光谱技术正成为目前研究开发的热点。该工作旨在探索一项水下激光诱导击穿光谱与激光拉曼光谱(LIBS-LRS)联合探测技术,以实现LIBS和拉曼两种检测技术在检测系统上的整合,在信息获取上的互补。在实验室搭建了一套LIBS-LRS联合探测装置,该装置对于拉曼和LIBS采用同样的激发光源、光谱仪和探测器,前置光路分为两部分:拉曼光路和LIBS光路,分别收集Na_2SO_4溶液的拉曼信号和LIBS信号。前置光路收集的拉曼和LIBS信号由Y型光纤导入光谱仪,分别在面阵CCD不同区域进行探测。利用该装置对配置的Na_2SO_4溶液进行探测,同时获得了Na元素的LIBS信号和SO^(2-)_4拉曼信号。另外,随着激光能量的提高,在532nm脉冲激光能量超过3.6mJ时,在拉曼光路同时获得了Na元素的LIBS信号和SO^(2-)_4拉曼信号,这样采用同一光路即可实现两种光谱技术的联合,然而实验发现,随着激光能量的增加,激光在溶液中击穿产生的轫致辐射造成了光谱探测基线整体的抬升,对拉曼光谱弱信号的探测是不利的。实验结果初步证明了在拉曼和LIBS在水下联合探测的可行性。

Spectroscopic sensor is becoming an important issue for the deep-sea exploration due to the advantages of multi-specie,multi-phases and stand-off detection.Different approach have been developing in recent years based on LIBS（Laser Induced Breakdown Spectroscopy）and Raman spectroscopy since Raman-LIBS are complementary techniques with the similar components and the capability of molecular and elementary analysis.In this work,we built a LIBS-Raman system and detected Na_2SO_4 in aqueous solution to evaluate the potential ocean application.With the same laser,spectrometer and detector,a hybrid of Raman and LIBS system was developed to realize the detection of anions and cations in the seawater.The optics was composed by two parts：Raman channel and LIBS channel,and the signal was collected by a Y type optical fiber bundle.The signal from two channels was separated by imaging on different arrays of the CCD detector.The Raman spectra of SO^（2-）_4and LIBS spectra of Na was successfully detected simultaneously when the pulse energy was above 3.6mJ.However,due to the strong bremsstrahlung radiation of LIBS,the signal to noise ratio of Raman was significantly decreased as the laser energy increasing.The results manifested the great potential of Raman-LIBS combination for the underwater detection.