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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Editor: James C. Wyant
  • Vol. 47, Iss. 27 — Sep. 20, 2008
  • pp: 4994–5006

Design and evaluation of a THz time domain imaging system using standard optical design software

Claudia Brückner, Boris Pradarutti, Ralf Müller, Stefan Riehemann, Gunther Notni, and Andreas Tünnermann  »View Author Affiliations


Applied Optics, Vol. 47, Issue 27, pp. 4994-5006 (2008)
http://dx.doi.org/10.1364/AO.47.004994


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Abstract

A terahertz (THz) time domain imaging system is analyzed and optimized with standard optical design software (ZEMAX). Special requirements to the illumination optics and imaging optics are presented. In the optimized system, off-axis parabolic mirrors and lenses are combined. The system has a numerical aperture of 0.4 and is diffraction limited for field points up to 4 mm and wavelengths down to 750 μm . ZEONEX is used as the lens material. Higher aspherical coefficients are used for correction of spherical aberration and reduction of lens thickness. The lenses were manufactured by ultraprecision machining. For optimization of the system, ray tracing and wave-optical methods were combined. We show how the ZEMAX Gaussian beam analysis tool can be used to evaluate illumination optics. The resolution of the THz system was tested with a wire and a slit target, line gratings of different period, and a Siemens star. The behavior of the temporal line spread function can be modeled with the polychromatic coherent line spread function feature in ZEMAX. The spectral and temporal resolutions of the line gratings are compared with the respective modulation transfer function of ZEMAX. For maximum resolution, the system has to be diffraction limited down to the smallest wavelength of the spectrum of the THz pulse. Then, the resolution on time domain analysis of the pulse maximum can be estimated with the spectral resolution of the center of gravity wavelength. The system resolution near the optical axis on time domain analysis of the pulse maximum is 1   line pair / mm with an intensity contrast of 0.22. The Siemens star is used for estimation of the resolution of the whole system. An eight channel electro-optic sampling system was used for detection. The resolution on time domain analysis of the pulse maximum of all eight channels could be determined with the Siemens star to be 0.7   line pairs / mm .

© 2008 Optical Society of America

OCIS Codes
(220.4830) Optical design and fabrication : Systems design
(110.6795) Imaging systems : Terahertz imaging

ToC Category:
Imaging Systems

History
Original Manuscript: April 23, 2008
Revised Manuscript: July 17, 2008
Manuscript Accepted: August 6, 2008
Published: September 18, 2008

Citation
Claudia Brückner, Boris Pradarutti, Ralf Müller, Stefan Riehemann, Gunther Notni, and Andreas Tünnermann, "Design and evaluation of a THz time domain imaging system using standard optical design software," Appl. Opt. 47, 4994-5006 (2008)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-47-27-4994

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