“Millimetre-waves” are electromagnetic radiation with frequencies between 30 and 300 GHz (corresponding to wavelengths between 1 cm and 1 mm). This spectral range is enclosed by the so-called “microwaves” – which are centimetre-waves, actually – with frequencies from 3 to 30 GHz (corresponding to wavelengths from 10 cm to 1 cm) and the so-called “Terahertz” range which covers the submillimetre-wave region between 300 GHz and 3 THz (corresponding to wavelengths between 1 mm and 0.1mm):

In our lab, we use backward wave oscillator (BWO) tubes manufactured by ISTOK (Moscow region, Russia) for the generation of coherent radiation within the millimetre- and submillimetre-wave range. The BWOs constructed for this high-frequency region are highly advanced devices, and each of them covers a wide band of frequencies with substantial RF output power, as shown in the table on the right:
BWO ModelFrequency Range/GHzOutput Power/mW
OB 24 177–263 20–50
OB 30 258–375 10–20
OB 32 370–535 4–15
OB 80 530–714 4–15
OB 81 690–850 4–15
OB 82 830–1030 3–10

For the operation of these BWOs, electromagnets (solenoids) with sizable magnetic field strengths (typically 1 T which is about 20,000 times the strength of earth’s magnetic field) are required (see the left picture below).
A mechanically sophisticated positioning device is indispensable to facilitate the alignment of the tube in the solenoid with the necessary precision (see the right picture below).
Furthermore, an exceptionally stable high-voltage power supply is needed, as well as a stabilization circuit to lock the tube to the desired frequency.

Electromagnet and BWO Positioning Device

In our lab, the BWO tubes are utilized in two different experimental setups:

  1. In a double resonance experiment we investigate intermolecular vibrations (bending and stretching of van der Waals bonds). Click the link below for further information about this technique.
  2. Currently, we are constructing a “terahertz spectrometer”, i. e. an absorption spectrometer that will allow us to measure rotational transitions in the above-mentioned (sub)mmw range. Click the link below for further information about this new spectrometer.

The Double Resonance Experiment     The Terahertz Spectrometer

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