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Proceedings Paper

Speckle reduction in THz imaging systems with multiple phase patterns
Author(s): Irina Jaeger; Johan Stiens; Gaetan Koers; Gert Poesen; Roger Vounckx
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Paper Abstract

THz technology makes possible imaging of phenomena, inaccessible to both visible and infrared radiation, but the imaging is still in its early stages of development. This paper draws attention to the aspects of speckle reduction to improve the image quality. Because all existing THz sources are coherent - speckle is an ultimate limiting factor of the free-space imaging techniques. Speckle arises when coherent light scattered from a rough surface is detected by an intensity detector with a finite aperture, hiding the image information. This problem is of special importance for THz imaging, because surface roughness is closer to the object dimension as in optical imaging. The reduction of speckle is highly desirable and we propose here a Hadamard matrix solution. Hadamard diffuser for mm-wave frequency range have been designed, built and tested. We report 50% speckle reduction measurements using a free-space vector network analyzer over the full W-band (75-110 GHz). The advantage of the mm-wave Hadamard technology over optical: the diffuser doesn't have to be moved (vibrated) any more to accomplish the technology of speckle reduction. Temporal optical effect is substituted here by spatial quasi-optical: Hadamard coding in each scan pixel. Second method delivers realistic system parameters for the speckle reduction with polychromatic light for aviation security.

Paper Details

Date Published: 19 April 2006
PDF: 8 pages
Proc. SPIE 6194, Millimeter-Wave and Terahertz Photonics, 61940B (19 April 2006); doi: 10.1117/12.662512
Show Author Affiliations
Irina Jaeger, Vrije Univ. Brussel (Belgium)
Johan Stiens, Vrije Univ. Brussel (Belgium)
Gaetan Koers, Vrije Univ. Brussel (Belgium)
Gert Poesen, Vrije Univ. Brussel (Belgium)
Roger Vounckx, Vrije Univ. Brussel (Belgium)

Published in SPIE Proceedings Vol. 6194:
Millimeter-Wave and Terahertz Photonics
Dieter Jäger; Andreas Stöhr, Editor(s)

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