The propagation and reflection of low energy phonons in liquid {sup 4}He with a free surface
The specular reflection of low energy phonons at the free surface of liquid {sup 4}He at {approximately} 0.05 K has been measured for angles of incidence between 20{degrees} and 80{degrees}. The distribution of the incident beam with respect to energy and direction is obtained from the theory of phonon decay using the curvature of the phonon spectrum measured by Rugar and Foster. The average incident phonon energy, at a distance of 2.3 cm from the source, is {approx} 0.3 K, which corresponds to an effective beam temperature of about 0.1 K. The reflection data are compared with the theory of Saam, modified to take into account the thermal ripplons at the surface. The theory predicts that the deviations from specular reflection are too small to be measurable. However there should be a broadening of {approximately} 1{degrees} in the reflected image of the phonon source (a heater) due to phonon decay. In agreement with the theory, the reflection is specular within the angular accuracy of {le} 2{degrees}. The reflection coefficient is unity within the experimental error of about 10%. The experiment was performed on liquid with the free surface containing 0.034 of a monolayer of {sup 3}He, however no effect from the {sup 3}He impurity was observed.
- OSTI ID:
- 375059
- Report Number(s):
- CONF-9304297-; ISSN 0003-0503; TRN: 96:004080-0451
- Journal Information:
- Bulletin of the American Physical Society, Vol. 40, Issue 2; Conference: 1993 joint meeting of the American Physical Society and the American Association of Physics Teachers, Washington, DC (United States), 12-15 Apr 1993; Other Information: PBD: Apr 1995
- Country of Publication:
- United States
- Language:
- English
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