# Selective reflection from Rb layer with thickness below $\lambda$/12 and applications

## TL;DR

This study investigates the unique optical properties of ultra-thin Rb vapor layers below 70 nm, revealing significant spectral shifts, broadening, and hyperfine splitting under magnetic fields, with potential applications in precision spectroscopy.

## Contribution

It demonstrates the effects of atom-surface interactions and magnetic fields on selective reflection in sub-wavelength Rb layers, a novel exploration of ultra-thin vapor cell optics.

## Key findings

- Observed a 240 MHz red shift and spectral broadening at 40 nm thickness.
- Resolved hyperfine Paschen-Back splitting into multiple components.
- Identified significant atom-surface interaction effects at nanoscale thicknesses.

## Abstract

We have studied the peculiarities of selective reflection from Rb vapor cell with thickness $L <$ 70 nm, which is over an order of magnitude smaller than the resonant wavelength for Rb atomic D$_1$ line $\lambda$ = 795 nm. A huge ($\approx$ 240 MHz) red shift and spectral broadening of reflection signal is recorded for $L =$ 40 nm caused by the atom-surface interaction. Also completely frequency resolved hyperfine Paschen-Back splitting of atomic transitions to four components for $^{87}$Rb and six components for $^{85}$Rb is recorded in strong magnetic field ($B >$ 2 kG).