Universität zu Köln

Langenbach, M., Roggenbuck, A., Mayorga, I. Camara, Deninger, A., Thirunavukkuarasu, K., Hemberger, J. and Grueninger, M. (2014). Group Delay in THz Spectroscopy with Ultra-Wideband Log-Spiral Antennae. J. Infrared Millim. Terahertz Waves, 35 (11). S. 918 - 932. NEW YORK: SPRINGER. ISSN 1866-6906

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Abstract

We report on the group delay observed in continuous-wave terahertz spectroscopy based on photomixing with phase-sensitive homodyne detection. We discuss the different contributions of the experimental setup to the phase difference Delta phi(nu) between transmitter arm and receiver arm. A simple model based on three contributions yields a quantitative description of the overall behavior of Delta phi(nu). Firstly, the optical path-length difference gives rise to a term linear in frequency nu. Secondly, the ultra-wideband log-spiral antennae effectively radiate and receive in a frequency-dependent active region, which in the most simple model is an annular area with a circumference equal to the wavelength. The corresponding term changes by roughly 6 pi between 100GHz and 1 THz. The third contribution stems from the photomixer impedance. In contrast, the derivative. partial derivative Delta phi/partial derivative nu is dominated by the contribution of periodic modulations of Delta phi(nu) caused by standing waves, e.g., in the photomixers' Si lenses. Furthermore, we discuss the Fourier-transformed spectra, which are equivalent to the waveform in a time-domain experiment. In the time domain, the group delay introduced by the log-spiral antennae gives rise to strongly chirped signals, in which low frequencies are delayed. Correcting for the contributions of antennae and photomixers yields sharp peaks or pulses and thus facilitates a time-domain-like analysis of our continuous-wave data.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Langenbach, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Roggenbuck, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Mayorga, I. Camara UNSPECIFIED UNSPECIFIED UNSPECIFIED Deninger, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Thirunavukkuarasu, K. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hemberger, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Grueninger, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-425213
DOI:	10.1007/s10762-014-0098-4
Journal or Publication Title:	J. Infrared Millim. Terahertz Waves
Volume:	35
Number:	11
Page Range:	S. 918 - 932
Date:	2014
Publisher:	SPRINGER
Place of Publication:	NEW YORK
ISSN:	1866-6906
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language TERAHERTZ; GENERATION; MILLIMETER Multiple languages Engineering, Electrical & Electronic; Optics; Physics, Applied Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/42521