Development of the 2-Dimensional Quasielastic Light Scattering Spectrometer

本研究项目的目的是开发一台二维准弹性光散射(2D-QELS)光谱仪，使我们能够获得各种材料微观涨落的详细信息。2D-QELS的测量方法是基于一种不同于2D-核磁共振和IR等2D光谱产生2D光谱的技术。1993年，我们组装了2D-QELS光谱仪，它由激光器、高压正弦波发生器、平行板电极池、外差模式光学混频系统以及带有光电倍增管和光子计数器的探测器单元组成。并用一个简单的光电二极管和A/D转换器系统对2D-QELS进行了透过性测量。1994年，我们在2D-QELS光谱仪和个人计算机之间建立了一个接口单元，并结合了一个基于推广的Wiener-Khinin定理的软件程序，使我们能够直接从散射光强获得2D光谱，而不需要计算自相关函数。然后将完成的2D-QELS光谱仪应用于水溶液中的聚苯乙烯胶乳和聚苯乙烯磺酸盐等标准样品。结果表明，与常规方法相比，该方法可以测量复电泳迁移率µ^*=muexp(IDelta)的相位增量，更准确地确定其幅值，并能在更宽的频率范围内检测到表观扩散常数D_(？)这种用于2D-QELS的新测量方法可望适用于各种周期平稳系统的含时波动。

The purpose of this research project is to develop a 2-dimensional quasielastic light scattering (2D-QELS) spectrometer, which enables us to obtain detailed information on the microscopic fluctuation of various materials. The measurement method for 2D-QELS is based on a different technique producing 2-dimensional (2D) spectra from other 2D spectroscopies such as 2D-NMR and IR.In 1993, we assembled the 2D-QELS spectrometer which consisted of a laser, a high-voltage sinusoidal wave generator, a cell with parallel-plate electrodes, an optical mixing system in the heterodyne mode, and a detector unit with a photomultiplier and a photon counter. And some perparatory measurements for 2D-QELS were performed by using a simpler system with a photodiode and an A/D converter. In 1994, we made an interface unit between the 2D-QELS spectrometer and a personal computer, and incorporated a software program based on an extended Wiener-Khinchin theorem, which enabled us to obtain the 2D spectra directly from the scattered light intensity without calculating the autocorrelation function. Then the 2D-QELS spectrometer completed was applied to standard samples such as a polystirene latex and polystirene sulfonate in aqueous solutions. As a result, it was found that we could measure the phase delta of the complex electrophoretic mobility mu^*=muexp (idelta), which was unobtainable by the conventional method, determine the value of the amplitude mu more acculately, and detect the apparent diffusion constant D_<app> in the frequency range wider than the conventional method. The new measurement method used in 2D-QELS is expected to be applicable to the time-dependent flucuations on various kinds of periodically stationary systems.