Laser holographic interferometry is an advanced precision measurement technology with sub-μm accuracy and large, over 17 mm, depth-of-field. The limitation of current laser holographic interferometry is the limited measurement area, which cannot be larger than the field of view (FOV). A hologram registration method without using targets is developed to overcome this problem. The theory of laser holographic interferometry, including the phase-shifting and multi-wavelength tuning, is described. The cross-correlation analysis is used to find the translation and overlapped regions, which determine the tilt and shift correction for data registration. The proposed method is validated using two examples with different approaches. The first example, a wheel hub, is smaller than the FOV and demonstrates only 0.1 μm discrepancy of the surface flatness between the registered and standard measurements. The second example, an engine combustion deck surface, is larger than the FOV. The registered surface measurements are compared to that of coordinate measurement machine (CMM) with only 2.5% discrepancy of the peak-to-valley flatness. This data registration method enables the sub-μm precision and large depth of field (several centimeters) measurement of large size objects.
Phase unwrapping for large depth-of-field 3D laser holographic interferometry measurement of laterally discontinuous surfaces
