Siegel der Universität

Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Superlattice spectrometer

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This experiment combines our phase locked Backward Wave Oscillators (BWO) with superlattice frequency multipliers. These new type of frequency multipliers generate higher odd harmonics of the fundamental radiation very efficiently.

Experimental Setup

The BWO is stabilized in frequency via a phase-locked loop (PLL) with respect to a rubidium reference with a frequency accuracy Δf/f=10-11. For detection of Superlattice output power below 2.33 THz, a magnetically tuned InSb hot electron bolometer (NEP=3.5 pW/√Hz) has been deployed, while a Ga-doped Ge photoconductor with significantly higher sensitivity (NEP=0.6 pW/√Hz) has been used for higher frequencies. A sketch of the spectrometer setup is shown in Fig.1. The main fraction of the fundamental output radiation generated by the BWO is coupled into the SL multiplier, and only a small fraction is used for the PLL circuitry. Two high-density polyethylene lenses focus the harmonics generated in the SL through a 3.5 m long absorption cell onto the detector. The detector signal is frequency selectively amplified, and demodulated by a lock-in amplifier. In all cases the 2f frequency modulation technique is used for recording spectra.

Schematic Setup of the Superlattice Spectrometer
Fig.1: Sketch of the spectrometer setup


Key Features

  • Spectral Range: 300 - 3100 GHz
  • Frequency Accuracy: Δf/f=10-11

Future Developments

  • Improvement of the output power of the radiation source
  • Improvement of the detector sensitivity


Dr. Frank Lewen
Christian Endres

Related Publications

C. P. Endres, F. Lewen, T. F. Giesen, S. Schlemmer, D. G. Paveliev, Y. I. Koschurinov, V. M. Ustinov, A. E. Zhucov
Application of Superlattice Multipliers for High Resolution THz Spectroscopy
Rev. Sci. Instr 78 , Art. No. 043106 (2007)


C. P. Endres, H. S. P. Müller, S. Brünken, D. G. Paveliev, T. F. Giesen, S. Schlemmer, and F. Lewen
High Resolution Rotation–Inversion Spectroscopy on Doubly Deuterated Ammonia, ND2H, up to 2.6 THz
J. Mol. Struct. 795 , 242–255 (2006)


S. Brünken, H. S. P. Müller, C. P. Endres, F. Lewen, T. Giesen, B. Drouin, J. C. Pearson, and H. Mäder
High Resolution Rotational Spectroscopy on D2O up to 2.7 THz in its Ground and First Excited Vibrational Bending States
Phys. Chem. Chem. Phys. 9 , 2103–2112 (2007)