Accession Number:

ADA270598

Title:

Acoustic Microscopy and Nonlinear Effects in Pressurized Superfluid Helium

Descriptive Note:

Technical rept.,

Corporate Author:

AEROSPACE CORP EL SEGUNDO CA ENGINEERING AND TECHNOLOGY GROUP

Report Date:

1993-08-31

Pagination or Media Count:

31.0

Abstract:

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 microscopes 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. We present arguments that the process underlying this nonlinear behavior is harmonic generation.

Subject Categories:

  • Inorganic Chemistry
  • Acoustics
  • Fluid Mechanics
  • Optics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE