Acoustic microscopy and nonlinear effects in pressurized superfluid helium. Technical report
The operation of an acoustic microscope having a resolution of 15 nm has been demonstrated. It uses as a coupling medium superfluid 4He colder than 0.9 K and pressurized to greater than 20 bar. The microscope is now being used to image objects that show little or no contrast on a scanning electron microscope. In addition, the acoustic microscope is being used to study the properties of sound propagation in the coupling fluid. At low acoustic intensities, the coupling fluid has very low acoustic attenuation at the microscope's operating frequency (15.3 GHz), but near the focal point the acoustic intensity can be high enough that the helium behaves with extreme nonlinearity. In fact, this medium is capable of entering new regimes of nonlinear interaction. Plots of the received signal versus input power display a nearly complete pump depletion at certain input power levels and a reconversion to the pump frequency at higher power levels. Such behavior has never before been observed. The authors present arguments that the process underlying this nonlinear behavior is harmonic generation. Cryogenic microscopy, Harmonic generation, Nonlinear acoustics.
- Research Organization:
- Aerospace Corp., El Segundo, CA (United States). Engineering and Technology Group
- OSTI ID:
- 5704553
- Report Number(s):
- AD-A-270598/6/XAB; TR-0091(6925-02)-1; CNN: F04701-88-C-0089
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
HELIUM
ACOUSTIC MICROSCOPY
HARMONIC GENERATION
SUPERFLUIDITY
SOUND WAVES
WAVE PROPAGATION
CRYOGENICS
HARMONICS
NONLINEAR PROBLEMS
TEMPERATURE RANGE 0000-0013 K
ELEMENTS
FLUIDS
FREQUENCY MIXING
GASES
MICROSCOPY
NONMETALS
OSCILLATIONS
RARE GASES
TEMPERATURE RANGE
665420* - Superfluidity- (1992-)
661210 - Cryogenics- (1992-)