We are presently interested in investigating the metastability of the condensed phases of Helium at low temperature (1K).
This is done by using a focused sound wave (1MHz) produced directly in the condensed phase : during the negative swings of the sound wave, the solid or liquid sample is brought for a short time at a pressure below its normal fusion or ebullition pressure. A sophisticated time resolved multiphase interferometric imaging technique produced phase maps of the sound field which are eventually converted in density maps around the acoustic focus.
In the case of solid, we observe an unexpected and yet unexplained instability of the metastable phase, at a pressure far above the spinodal limit below which the solid cannot exist. In the case of liquid we observe cavitation of bubbles at a density which seems to correspond to a higher pressure (nearer the ebullition pressure) than was previously determined by S. Balibar, F. Caupin and co-workers
info aucun article