提出一种基于离轴数字全息显微的技术, 用于测量液态环境中微粒的三维位置。该技术采用透射式离轴数字全息显微系统, 测量方法结合了光程长(OPL)差分算法和去条纹法。利用光程长差分算法定位微粒内部两点间光程长差分曲线拐点的位置, 追踪微粒的轴向位移; 对离轴全息图使用去条纹方法, 即频域滤波结合Hough变换, 获取微粒的横向二维位移。进行轴向测量时, 与传统数字全息追踪微粒位移的技术相比, 光程长差分算法仅用两点光程长相对运算代替面的运算, 提高了测量效率, 且不需要对微粒进行自动聚焦, 微粒的位置也不受离焦面的限制。对微粒进行纳米级三维位移操纵, 实验结果表明光程长差分算法结合去条纹法对液态环境中微粒的三维位移测量分辨能力能够达到纳米量级。

A technique based on off-axis digital holographic microscopy is proposed to measure three-dimensional position of particle in a liquid environment. The technique uses the transmitting off-axis digital holographic microscopy system, and the method combines the optical path length (OPL) difference method and fringe removing method. The OPL difference method is used to measure the axial position of the particle by locating the inflection point of OPL difference curves of two specific points in the particle. The fringe removing method is utilized for the off-axis holograms to measure the in-plane displacement of the particle with frequency filtering and Hough transform combined. Compared to the traditional digital holographic particle tracking techniques, the OPL difference method applies the OPL between two points to relative calculation instead of plane calculation. As a result, the measurement efficiency is improved, auto-focusing of particles is not needed, and the particle position is not constrained by the defocusing plane. The experimental results of nano-scale three-dimensional particle measurement show that the resolution ability reaches nano-scale when the OPL difference method is combined with the fringe removal method to measure the three-dimensional displacement of particles in the liquid environment.