Surface Characterization by the Use of Digital Holography

Abstract

Digital holography (DH) is an attractive measuring optical technique in the fields of engineering and science due to its remarkable accuracy and efficiency. The holograms are recorded by an interferometer and reconstructed by numerical methods such as Fresnel transform, convolution approach, and angular spectrum. Because harmful coherent noise often arises when long coherent lengths are used, bright femtosecond pulse light with ultrashort coherent length may be the solution to reduce both spurious and speckle noises. Since the usual DH uses a visible light, it is difficult to visualize 3D internal structure of visibly opaque objects due to their limited penetration depth. The terahertz (THz) radiation has a good penetration capability; thus, 3D visualization of both surface shape and internal structure in visibly opaque object can be achieved via THz-DH technique.

Surface Characteristics Measurement Using Computer Vision: A Review

“…o Disadvantages: low speed of measurement, low resolution [83]. [90]. o Disadvantages: slower process, used for small objects, and does not change resolution [91].…”