Nonlinear acoustic interactions in superfluid helium

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:5754945

Wright, D R

Studies of nonlinear acoustic interactions in superfluid helium at temperatures below 0.2{degree}K have culminated in the construction of an all-acoustic parametric amplifier at gigahertz frequencies. This amplifier represents the shortest wavelength parametric amplifier ever made, with signal wavelengths shorter than 1000 {angstrom} and pump wavelengths shorter than 600 {angstrom}. Begun as part of a program to extend the frequency range, and hence improve the resolution, of the scanning acoustic microscope while maintaining an adequate signal-to-noise ratio, the early work on nonlinearity concentrated on the very high power densities achieved at the focus of an acoustic lens. In a pressure range where the dispersion forbids three-phonon processes, indirect evidence of four-phonon mixing is observed. In the parametric amplifier experiment, plane waves are mixed at a predefined angle in the superfluid helium. Two gain regimes are observed. The first regime is a four-phonon collinear process, in which gain on the signal is created by the second-harmonic of the pump. The second 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.

• Research Organization: Stanford Univ., CA (USA)
• OSTI ID: 5754945
• Country of Publication: United States
• Language: English

Related Subjects

640450* -- Fluid Physics-- Superfluidity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AMPLIFICATION
AMPLIFIERS
ELECTRONIC EQUIPMENT
EQUIPMENT
EVEN-EVEN NUCLEI
FLUIDS
GAIN
HELIUM 4
HELIUM II
HELIUM ISOTOPES
INTERACTIONS
ISOTOPES
LIGHT NUCLEI
NONLINEAR PROBLEMS
NUCLEI
PARAMETRIC AMPLIFIERS
PHONONS
QUANTUM FLUIDS
QUASI PARTICLES
SOUND WAVES
STABLE ISOTOPES
SUPERFLUIDITY
ULTRALOW TEMPERATURE