针对表面高度起伏较大的物体的三维形貌测量问题，提出了一种改进的离轴双波长数字全息测量方法。利用偏振分光原理，将两个波长的物光信息同时记录在一幅全息图上，并借助两个波长的频差形成远大于单一波长的等效波长，从而将数字全息术的纵向测量范围拓展到微米甚至毫米量级范围，有效克服了单波长数字全息术测量形貌起伏较大物体时不可避免的相位去包裹问题。对微米量级高度起伏的台阶状样品形貌进行了实验测量，测量结果与样品标称值及台阶仪测量值具有很好的一致性，证明了该方法的有效性。

An improved off-axis dual-wavelength digital holography method is presented for three-dimensional surface topography measurement of objects with significant variations. The object beams informations of the two different laser wavelengths are recorded on one hologram based on polarization splitting principle, thus the measurement range can be expanded to micron or millimeter scales by means of the equivalent wavelength induced by difference frequency effect between the two wavelengths and the equivalent wavelength is longer than any single one. So the problems of inevitable phase unwrapping when the object morphology with significant variations are measured by a single wavelength is overcame effectively. The morphology of a staircase sample with micron height variations is measured. The experimental results are consistent with the nominal values and the values measured by profile-system, which shows the effectiveness of the proposed method.