动态光散射系统最佳光接收孔径比研究

The Study of Best Receiver Aperture Ratio in Dynamic Light Scattering System

从动态光散射(Dynamic Light Scattering,DLS)光接收系统的空间相干性出发,推导了干涉信号的表达式并对系统的噪音进行了全面的分析.在环境温度恒定且光电倍增管(Photomultipier Tube,PMT)良好冷却的条件下,PMT的泊松随机噪音为系统主要噪音.利用光子统计理论推导了PMT的噪音,得到其输出的功率信噪比并计算了功率信噪比最大时的接收孔径比.实验表明,通过调整两固定孔间的距离,PMT输出的功率信噪比可达到最大.由不同孔径比实验计算得到的自相关函数证明了理论的合理性.

The receiver area of Photomuhipier Tube （PMT） must be smaller than the coherence area,which is the only criterion of detector aperture in Dynamic Light Scattering （DLS） system,other than a definite size of receiver aperture. The noise of the DLS system is analysed, the Poisson Noise of PMT is the main noise of the system under the condition that the temperature of the surrounding is invariable and the PMT is cooled well. The signal-to-noise power ratio （S^2/N^2） of the PMT is deduced based on spatial coherence and statistics of photon and the best receiver aperture ratio is calculated under the condition that S^2/N^2 is the biggest. Furthermore, with two given pin holes, the biggest S^2/N^2 can be reached by adjusting the distance between them. Finally, the theory conclusion is proved through the test of autocorrelation curve with different receive aperture ratio.