Dresden 2009 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 6: Poster I

DF 6.4: Poster

Dienstag, 24. März 2009, 09:30–12:30, P5

Development of a precisely tuneable continuous-wave THz spectrometer with interferometric frequency control — •Holger Schmitz¹, Joachim Hemberger¹, Anselm Deninger², Axel Roggenbuck², and Markus Grüninger¹ — ¹II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany — ²TOPTICA Photonics AG, Lochhamer Schlag 19, D-82166 Gräfelfing, Germany

We will report on the development of a precisely tuneable continuous-wave THz spectrometer with interferometric frequency control. The system is based on mixing two near-infrared distributed feedback diode lasers, the beat of which can be tuned continuously from 0 to 1.2 THz. Each laser is stabilized by electronic feedback from a low-finesse Fabry-Perot etalon, yielding a laser linewidth of roughly 1 MHz and a frequency precision of a few MHz. The laser beat is converted into THz radiation by a photoconductive switch, which efficiently generates THz radiation from 20 GHz to 1.2 THz. The THz radiation is detected via a second photoconductive switch via homodyne mixing of the THz signal and the laser beat. The coherent homodyne detection preserves the phase information of the THz electric field, so that both the real and the imaginary part of the dielectric function, ε₁ and ε₂, can be determined. Making use of different optical path lengths for the laser beam and the THz radiation, the phase shift due to the sample can be determined by sweeping over an interference fringe, typically a few 100 MHz. Thus ε₁ and ε₂ can be determined without mechanically moving parts. First results obtained with this system will be reported.