Development of measurement techniques of three dimensional velocity around a microbe by using a differential interference contrast microscope

为了测量微生物周围的速度分布，研制了一种带有差动干涉衬度(DIC)显微镜的三维粒子跟踪速度计(3D PTV)。该方法利用粒子散焦图像的特性来估计粒子到焦平面的距离。在粒子的散焦图像中，在粒子图像的中心周围产生环状图像，并且随着粒子到焦平面的距离增大，环状图像的直径增大。实验结果表明，环形像的直径与粒子到焦平面的距离成正比。该方法已应用于水中粒子布朗运动的测量。计算结果与理论预测吻合较好。

To measure velocity distributions around a microbe, the three dimensional Particle Tracking Velocimetry (3D PTV) with a Differential interference contrast (DIC) microscope has been developed. In this method, the properties of out-of-focus image of particle are used for estimation of distance from particle to focal plane. In the out-of-focus image of particle, a ring like image is generated around the center of the particle image and the diameter of the ring like image increases with the distance from the particle to focus plane. Experimental results show that the diameter of the ring like image is proportional to the distance from a particle to the focal plane.The proposed method has been applied to measurements of the Brownian motion of a particle in water. The Results show a good agreement with the theoretical prediction.