Competing van der Waals and dipole-dipole interactions in optical nanocells at thicknesses below 100 nm

To reliably register the absorption or selective reflection of laser radiation in a nanocell filled with a vapor of Cesium or Rubidium at thicknesses below 100 nm, it becomes necessary to increase the atomic density by heating the cell. It is shown that both atom-wall van der Waals (vdW) interactions and Dipole-Dipole (DD) Lorentz-Lorenz interactions cause a similar "red" shift in the frequency of resonances of about the same order, which largely increases the total frequency shift. Previously, unaccounted-for DD interaction led to an overestimation of the value of the C3 coefficient of the vdW interaction. We show for the first time that varying the nanocell thickness between 130 nm and 30 -50 nm leads to a decrease of the C3 computed from the vdW "red" shift, i.e. we observe experimentally the so-called "retardation" of the vdW effect recently predicted in theoretical papers. The measurements were made using our unique nanometric-thin cells.& COPY; 2023 Elsevier B.V. All rights reserved.