In this presentation, a review and quasioptical imaging system and design considerations for an off-axis parabolic mirror based THz imaging systems are presented. It is shown that off-axis parabolic mirrors introduce off-axis intensity and polarization distortion. When a train of OAPs are used to relay THz beam, each distortions rapidly stacks to produce quite ugly beam and polarization profile. We show that the distortion of field distribution and polarization as a function of mirror curvature and focusing parameters. A brief review of design rules are shown to eliminate these distortions by a symmetric configurations of off-axis parabolic mirror train. The detrimental distortion effects were cancelled out by orienting the final two mirrors in a way to that recovers the original source profile. Comparisons of field profiles between compensated and uncompensated design are shown and imaging performance on characterization targets presented. In addition to benefits in field and polarization distribution the improved design facilitates 1D scanning with minimal change to overall optical path length.

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Shijun Sung and Zachary Taylor, "Quasioptical imaging system design for THz medical imaging application (Conference Presentation)," Proc. SPIE 9706, Optical Interactions with Tissue and Cells XXVII, 970605 (Presented at SPIE BiOS: February 14, 2016; Published: 3 May 2016); https://doi.org/10.1117/12.2218578.4868462755001.