Title: High-energy phonon pulses in liquid<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow /><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:math>
Abstract: We have discovered a method for selectively detecting high-energy phonons which has enabled us to make detailed measurements of the shapes of high-energy phonon pulses in liquid ${}^{4}\mathrm{He}$ at $\ensuremath{\approx}50\mathrm{mK}.$ These phonons are created from pulses of low-energy phonons, injected into the helium by a heater. We suppress the detection of the low-energy phonons by orienting a thin film superconducting Zn bolometer at an angle to the phonon beam. We find that the high-energy phonons are created continuously along the propagation path. As there is also velocity dispersion, the signal at any time is due to a range of phonon energies. Computer simulations of the signals from short pulses reproduce the main features of the measured results. The behavior of the high-energy phonon signals as functions of heater power and pulse length are analyzed and this leads us to suggest how the low-energy phonon pulse develops. In the following paper [I. N. Adamenko et al., Phys. Rev. B 69, 144525 (2004)] the pulse shape for short pulses is derived analytically.
Publication Year: 2004
Publication Date: 2004-04-30
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 37
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