Cross polarization in swept beam THz imaging systems using off-axis parabolic mirrors
Pouyan Rezapoor (Aalto University)
Aleksi Tamminen (Aalto University)
Aleksi Tamminen (Aalto University)
Juha Ala-Laurinaho (Aalto University)
Nuria Llombart (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Helena Rodilla (Chalmers University of Technology)
Jan Stake (Chalmers University of Technology)
Zachary D. Taylor (Aalto University)
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Abstract
The optical behavior of a terahertz imaging system employing a train of four identical off-axis parabolic mirrors with oblique incidence angle illumination is investigated in this work. The aperture filling and aberrations of a single off-axis parabolic mirror when illuminated by a Gaussian terahertz beam at its focus point is measured and simulated. The amplitude of E-field in transverse electric (TE) and transverse magnetic (TM) polarizations at target plane reveals a significant cross polarization, even when there is zero cross polarization at the source beam, amplitude of which is ∼ 33% of TE polarization. The investigation of the E-field on the detector plane reveals that this ratio is ∼ 1.5% at the detector plane, and the cross polarized E-field at the target plane is rotated back to co polarization. Although its amplitude is negligible, the TM distribution at detector plane is bimodal and tilted about the optical axis.