Answers are grounded in this paper and cite their sources.
Ellipsometric measurements of the thickness of the surface of liquid 4 He are reported for temperature from 1.4 to 2.3 K. The vertical thickness t within which the density changes from 90 to 10% of the bulk liquid density increases slightly with temperature from 1.4 to 2.1 K, having an average value of 9.4 AA at 1.8 K. There is some evidence of a rise of 2 or 3 AA between 2.1 K and the lambda -point.
No takes yet. Share an insight, caveat, or question.
D V Osborne (1989) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: