Holographic detection for fast fringe projection profilometry of deep micro-scale objects.

Phase-shifting Fringe projection profilometry (FPP) excels in 3D measurements for many macro-scale applications, but as features-of-interest shrink to the microscopic scale, depth-of-field limitations slow measurements and necessitate mechanical adjustments. To address this, we introduce digital holography (DH) for fringe image capture, enabling numerical refocusing of defocused object regions. Our experiments validate this approach and compare depth measurement noise with other DH and FPP methods. Results show that for slight defocus, incoherent FPP surpasses coherent techniques, while under significant defocus, the new method minimizes measurement uncertainty and matches the performance of other DH techniques, facilitating faster measurement of deep, micro-scale objects.