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Digital holographic imaging for free surfaces of superfluid helium

Vitor S. Barroso1,*, Patrik Švančara1,†,‡, Chris Goodwin1, Sreelekshmi C. Ajithkumar2,§, Ilaria Dimina1, Silvia Schiattarella2, Pietro Smaniotto1, Leonardo Solidoro1, Marion Cromb1 et al.

Radivoje Prizia2,∥, Anthony J. Kent2, and Silke Weinfurtner1,3,4

  • 1School of Mathematical Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom
  • 2School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom
  • 3Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, United Kingdom
  • 4Photon Science Institute, Alan Turing Building, University of Manchester, Manchester, M13 9PY, United Kingdom

  • *Contact author: vitor.barroso.s@outlook.com
  • patrik.svancara@neel.cnrs.fr
  • Present address: Institut Néel, CNRS-UGA, 25 avenue des Martyrs, 38042 Grenoble, France.
  • §Present address: Department of Physics, University of Strathclyde, Glasgow, G4 0NG, United Kingdom.
  • Present address: Laboratoire Kastler-Brossel, Sorbonne Université, ENS-Université PSL, CNRS, Collège de France, 4 place Jussieu, 75005 Paris, France.

Phys. Rev. Applied 26, 014080 – Published 24 July, 2026

DOI: https://doi.org/10.1103/dh9b-k6hm

Abstract

Visualizing the free surface of superfluid helium offers a rare opportunity to explore wave dynamics in the limit of vanishing viscosity. Such measurements are nonetheless challenging due to helium’s low refractive index contrast, restricted optical access to the cryogenic setups required to maintain helium in its superfluid phase, and mechanical vibrations from the various cooling stages. Overcoming these limitations will enable quantitative studies of surface-wave dynamics with applications in fluid mechanics, quantum simulation, and quantum optomechanics. Here, we report an implementation of off-axis digital holography for full-field imaging of the free surface of superfluid He4. We perform noncontact measurements of nanometer- to micrometer-scale interface fluctuations in two cryogenic systems: a traditional helium bath cryostat and a cryogen-free refrigerator. We employ machine-learning-based analysis to isolate noise-driven normal modes and their spatial structure in both systems. This enables reconstruction of the dispersion relation for gravity-capillary waves in macroscopic samples and, for thick films, determination of the film thickness from the measured dispersion, providing a quantitative benchmark for our approach. These proof-of-concept experiments show that digital holography is a powerful and versatile tool for high-resolution, minimally invasive studies of superfluid surfaces, with strong potential for integration into diverse experimental platforms.

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