Electronic Resource
[S.l.]
:
American Institute of Physics (AIP)
Journal of Applied Physics
68 (1990), S. 4438-4445
ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Studies of nonlinear acoustic interactions in superfluid helium at temperatures below 0.2 K have culminated in the construction of an all-acoustic parametric amplifier at gigahertz frequencies. This device represents the shortest wavelength parametric amplifier ever made, with signal wavelengths shorter than 1000 A(ring) and pump wavelengths shorter than 600 A(ring). In the experiment, plane waves are mixed at a predefined angle in the superfluid helium. Two gain regimes are observed. The first regime is a noncollinear phase-matched process, in which the signal phonon stimulates decay of the pump phonon to create gain at the signal frequency. The second regime is a four-phonon collinear process, in which gain on the signal is created by the second harmonic of the pump. This four-phonon process is unusual and is shown to be a combination of three-phonon processes wherein the lack of conservation of energy and momentum in one process is mostly compensated by the other.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.346194
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