Abstract
We photographed a transient evaporation under the cryogenic condition, around 2 K, where a very 'pure' system is obtainable to observe an evaporation phenomena because nothing but helium exists in the form of liquid. The phenomena was very fragile, just causing a quote small variation in density. The photos of evaporation, which was induced by a thermal wave incident on the vapor-liquid interface of superfluid helium (HeII), were taken in use of the holographic interferometer with a pulsed ruby later. The superfluid helium has a peculiar character that thermal conduction is carried out in the form of wave, not being in the form of diffusion. Taking advantage of this character, we heated up the vapor-liquid interface of liquid helium by a plane thermal wave, uniform heating parallel to the interface being attainable by generating the thermal wave with a plane heater installed in the liquid, propagating in there and getting incident on the interface. In this paper, we observed the behavior of the evaporation by a thermal wave and measured its propagating speed and density variation with various heat flux from the heater. The infinite fringe interferogram method was mostly adopted just for visualization while the finite fringe interferogram method was utilized for quantitative measurement.
