Construction details of a low-temperature raster system for moving crystals with a maximum size of 14 mm × 14 mm × 14 mm over a small area of piezoelectric sound excitation are described. The pure mechanical raster system in the liquid helium is driven by two stepping motors outside the cryostat. The minimum step size is 1 μm and the maximum raster area 14 mm×14 mm. This raster system was used in sound-beam topography at a frequency of 70 GHz. For this purpose, a special quasioptical transmission line across the dewar wall was also developed which is briefly described together with the applied electromechanical transducer system.
We report on successful application of frequency modulation–continuous wave (FM-CW) technique in sound-echo experiments at microwave frequencies. As an electromagnetic source, a reflex klystron with only 100 mW CW power or even less is sufficient to produce outstanding spectral echo signals in the kHz frequency range using homodyne detection. In contrast to the common pulse-echo technique in the GHz range, there is no need of a high power source like a magnetron and no need of a separate local oscillator that is essential in heterodyne detection. The FM-CW technique seems to be a very promising method for sound experiments at still higher frequencies.
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