Digital holography and coherent imaging are explored in the terahertz frequency region at 0.480 Terahertz with highly coherent, frequency-tunable continuous wave sources. The long coherence length of microwave sources suggests that interferometric imaging techniques such as Fresnel off-axis holography can achieve sub-micrometer depth resolution of surfaces and through materials and structures that are transmissive in the terahertz spectral region. Research in this area will provide an important non-destructive imaging tool for the rapidly expanding field of additive manufacturing and composite fabrication. Unfortunately, imaging optics as they are used in confocal imaging and optics in general adversely affect the performance of terahertz imagers as their aperture size if comparable to the wavelength, which artificially limits image resolution according to the diffraction limit and can cause undesirable coherence effects in the image. We report on imaging methods that minimize the use of optics but use signal processing techniques that form images digitally from recorded holograms. This approach is directly applicable to focal plane arrays in contrast to confocal imaging modalities. Furthermore, the performance of image reconstruction at multiple aspect angles compiled into videos as user friendly inspection tool is investigated.

Date Published: 2 June 2017
PDF: 12 pages
Proc. SPIE 10209, Image Sensing Technologies: Materials, Devices, Systems, and Applications IV, 102090C (2 June 2017); doi: 10.1117/12.2266360

Published in SPIE Proceedings Vol. 10209:
Image Sensing Technologies: Materials, Devices, Systems, and Applications IV
Nibir K. Dhar; Achyut K. Dutta, Editor(s)