Low Temperature Physics: 34, 254 (2008); https://doi.org/10.1063/1.2911649 (8 pages)
Interaction between microwave electromagnetic waves and superfluid current in He II
A.S. Rybalko1, S.P. Rubets1, E.Ya. Rudavskii1, V.A. Tikhiy1, R. Golovashchenko2, V.N. Derkach2, and S.I. Tarapov2
1B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Lenin Ave., Kharkov 61103, Ukraine
2A. Usikov Institute of Radiophysics and Electronics of the National Academy of Sciences of Ukraine 12 Acad. Proskura Str., Kharkov 61085, Ukraine
Received December 17, 2007
The absorption of electromagnetic waves is studied experimentally in liquid helium in a frequency range 40–200 GHz at temperatures of 1.4–2.8 K. The spectrum of «whishpering gallery» of fluctuations modes was registered in a dielectric disk resonator immersed in liquid helium. Superfluid currents in He II were stimulated by two «thermal guns». A narrow line of UHW wave absorption was observed at the frequency of single-roton excitation. It is found that with increasing the superfluid current velocity vs the character of the resonance line changes drastically: the absorption of UHW photons is replaced by their stimulated radiation, as seen from the sharp amplification of the high-frequency signal. This effect can be explained within the framework of the two-level model of He II. A stepwise change of superfluid velocity is observed with a continuous increase in the power supplied to the heater gun, what can argue in favor of quantization of vs. It is shown that the superfluid current has a low-frequency influence on UHW wave, which manifests itself externally as a modulation of UHW oscillations. Possible reasons for this effect are analyzed.
PACS: 67.10.Hk Quantum effects on the structure and dynamics of non-degenerate fluids;
Key words: superfluid helium, dielectric resonator, wishpering gallery.