Low-coherence optical profilometry with multi-reflection reference mirrors for large-depth object measurement.

A new, to the best of our knowledge, optical configuration for digital holographic profilometry for surface profile measurement of large-depth objects is proposed. Two multi-reflection mirrors were employed to extend the maximum axial measurable range by a factor of 2 without any degradation of the spatial resolution. By adjusting the distance and the position of the two multi-reflection reference mirrors, the system can be made more flexible for measuring different parts of the object. In addition to the axial extension, the two-mirror system also increases the visibility of the interference fringes so that the object profile can be measured with high accuracy.