Experiments on the decay instability of gravity-capillary waves excited by alternating electric fields with frequencies of 14-30 Hz on a charged liquid hydrogen surface in a rectangular cell are reported. An exponential increase in the amplitudes of the subharmonics caused by decay of the wave at the pump frequency is found. For the first time, the experimentally observed growth rate of the decay instability and damping coefficient for the surface waves in the rectangular cell yield an estimate of the coefficient for three-wave interactions of gravity-capillary waves in liquid hydrogen.
The results of experimental studies of wave turbulence in a system of capillary waves formed on the surface of liquid hydrogen at a tempera-ture of 15 K in a cylindrical cell with monochromatic radially symmetric pumping are presented. The local maximum formation with adecrease in the pumping amplitude was observed for thefirst time in the high-frequency region of the inertial range of the stationary turbu-lent spectrum at the direct cascade edge. The occurrence of a local maximum can be associated with a significant manifestation of viscousdamping in the high-frequency region of the spectrum.
We report on the experimental observation of energy accumulation near the high frequency boundary of the inertial range in the spectrum of turbulence in a system of capillary waves on the surface of liquid hydrogen driven by a harmonic force. The effect is manifested as a local maximum in the spectrum of pair correlation function of the surface elevation. This phenomenon is dynamical and can be seen only during reconfiguration of the turbulent cascade caused by waves generation of below the driving frequency.
Superconducting nanowire single-photon detectors (SNSPD) are used in quantum optics when record-breaking time resolution, high speed, and exceptionally low levels of dark counts (false readings) are required. Their detection efficiency is limited, however, by the absorption coefficient of the ultrathin superconducting film for the detected radiation. One possible way of increasing the detector absorption without limiting its broadband response is to make a detector in the form of sev- eral vertically stacked layers and connect them in parallel. For the first time we have studied single- photon detection in a multilayer structure consisting of three superconducting layers of amorphous tungsten silicide (WSi) separated by thin layers of amorphous silicon. Two operating modes of the detector are illustrated: an avalanche regime and an arm-trigger regime. A shift in these modes occurs at currents of ?0.5–0.6 times the critical current of the detector. Published
Formation of low frequency harmonics on turbulent distribution in the system of waves on the surface of liquid hydrogen has been studied in the frequency range 1-100 Hz (capillary-gravity waves). It is shown that the geometry of the experimental cell has a significant influence on the direct cascade of capillary waves generated by monochromatic force as well as on the direction of the wave energy transfer from the range of pumping towards that of dissipation. Besides a direct turbulent cascade, single half-frequency harmonic generation was observed in a cylindrical cell under high pump power. In a square cell we observed not only a half-frequency harmonic but a number of low frequency harmonics below the driving frequency generated by the nonlinear three-wave interaction. In the case of a rectangular cell we observed formation of incommensurate low frequency harmonics caused by the three-wave interaction of capillary waves and generation of a wave mode of similar to 1Hz in the frequency range of gravity waves which could be attributed to the four-wave interaction.