光散射谱学在地球内部物质弹性波速测量中的应用与展望

Review on Application of Optical Scattering Spectroscopy for Elastic Wave Velocity Study on Materials in Earth's Interior

高温高压下地球内部物质弹性波速的实验测量数据,可直接与地震波观测结果相结合,对地球内部的组成、状态和物质运移方式等进行反演,是了解地球深部信息的重要手段。在金刚石压砧(diamond anvil cell,DAC)中利用布里渊散射对矿物波速进行原位测量,是人们研究地球各圈层弹性性质的重要方法。随着DAC实验技术发展,一方面,可以获得模拟地球各圈层的极高温压条件;另一方面,DAC的光学特性使得各种光学分析和测试方法得到了广泛的应用。要获得高温高压下的弹性波速,首先需要对样品腔中的实验压力和加热温度进行精确的标定和测量;其次需对散射信号进行处理,通过布里渊散射频移,求出样品中的波速;最后结合X射线技术获得的晶格常数,可由固体弹性理论解出矿物的各弹性参数。重点介绍了布里渊散射和拉曼散射等光谱学方法在弹性波速实验研究中的应用,阐述了它们在波速测量、压力和温度标定等方面的基本原理和研究进展。分析了两种光谱学定压方法(荧光光谱压标和拉曼光谱压标)的定压方式和适用范围,以及两种主要的光谱学温标(黑体辐射温标和拉曼光谱温标)在温度测量中的应用。最后,回顾了基于光谱学测量建立起来的布里渊散射系统对下地幔主要矿物(钙钛矿、方镁铁矿、斯石英等)弹性波速测量取得的新成果,深入讨论了它们的地球物理意义,并对其未来的发展进行了展望。

In-situ experimental results on the elastic wave velocity of Earth materials at high pressure and high temperature in combination with data from seismic observation can help to inverse the chemical composition,state and migration of materials in Earth’s interior,providing an important approach to explore information of deep earth.Applying the Brillouin scattering into the Diamond Anvil Cell （DAC）to obtain the in situ elastic wave velocities of minerals,is the important approach to investigate elas-tic properties of Earth’s Interior.With the development of DAC technology,on the one hand,the high temperature and high pressure experimental environment to simulate different layers of the earth can be achieved;on the other hand,the optical prop-erties of DAC made many kinds of optical analysis and test methods have been widely applied in this research field.In order to gain the elastic wave velocity under high temperature and high pressure,the accurate experimental pressure and heating tempera-ture of the sample in the cavity should be measured and calibrated first,then the scattering signal needs to dealt with,using the Brillouin frequency shift to calculate the velocity in the sample.Combined with the lattice constants obtained from X ray tech-nique,by a solid elastic theory,all the elastic parameters of minerals can be solved.In this paper,firstly,application of methods based on optical spectrum such as Brillouin and Raman scattering in elasticity study on materials in Earth’s interior,and the bas-ic principle and research progress of them in the velocity measurement,pressure and temperature calibration are described in de-tail.Secondly,principle and scope of application of two common methods of spectral pressure calibration （fluorescence and Ra-man spectral pressure standard）are analyzed,in addition with introduce of the application of two conventional means of tempera-ture calibration （blackbody radiation and Raman temperature scale）in temperature determination.Lastly,geophysical applica-tions of mineral elasticity are discussed on the basis of the recent research results derive from Brillouin scattering system of wave velocities for major minerals in Earth’s lower mantle （perovskite,ferropericlase,etc.）,and the future research work is inspec-ted.