IMAGING THE EDGE OF A HE-4 PREWETTING FILM ON A CESIUM METAL, SURFACE

The edge of a metastable He-4 prewetting film on a cesium metal surfac e is investigated using polarization interference microscopy. This tec hnique images the local gradient of the coverage through its optical t hickness. The cesium metal is a film evaporated on a polished copper s ubstrate. A liquid helium film is deposited on the surface through rai sing and lowering the bulk liquid surface. Its edge is clearly observe d for temperatures below 1.6 K. The apparent optical thicknesses of th e films, larger theta what is expected for a normal saturated film, re main to be explained.