Effects of inert background gases and photo-illumination on three-color electromagnetically induced transparency of rubidium vapor

TL;DR

This work investigates three-color Rydberg-EIT in room-temperature rubidium vapor mixed with inert gases ($Ar$, $Ne$, $N_2$) at 50 and 500 mTorr, revealing pressure-dependent shifts and blue-shifted satellite lines arising from hyperfine collisions with the $5D_{3/2}$ state. By tuning the principal quantum numbers ($n=25$ and $n=50$) and employing RF dressing, the authors map the spectral response, including how satellite strengths grow with pressure while their separations remain largely unchanged, and how the spectra are altered by dc electric fields generated via photo-illumination with a $453$-nm laser. The inert-gas background also suppresses photo-induced electric fields, significantly reducing Stark shifts and enabling stable EIT signals under illumination; Ar at low pressure emerges as a particularly favorable medium for field diagnostics. The results advance non-invasive electric-field sensing in mixed-species warm vapors and suggest practical pathways for plasma-field diagnostics and spectroscopy in low-pressure inert-gas environments. Potential extensions include applications to plasma diagnostics, exploration of other alkali–inert gas mixtures, and development of robust, field-sensitive Rydberg sensors for real-world environments.

Abstract

Three-color Rydberg electromagnetically induced transparency (EIT) of room-temperature Rb vapor in the presence of inert gases (Ar, Ne, and N$_2$) at 50~mTorr and 500~mTorr is investigated. The observed EIT lines shift and develop blue-detuned satellite lines, dependent on inert-gas species and pressure. The separations of the satellite from the main EIT lines are approximately pressure-independent, while their strength increases with inert-gas pressure. The satellite lines are attributed to hyperfine collisions of the intermediate $5D_{3/2}$ state. Further, analyzing the Stark effect of Rydberg levels, it is found that the inert gases suppress static electric fields in the vapor cells, which we induce by photo-illumination of the cell walls with an auxiliary 453-nm laser. In the work, we utilize Rydberg levels with principal quantum numbers $n$ = 25 and 50 and angular momenta $\ell$ = 3 up to 6, excited by the EIT lasers and optional radio-frequency dressing fields. The work is of interest in the spectroscopic study of mixed-species warm vapors, in sensing applications of Rydberg atoms in vapor cells, and in non-invasive electric-field diagnostics of low-pressure discharge plasma.

Figures (3)

• Figure 1: (a) Sketch of the experimental setup, with a cross-sectional view provided in the inset (DM = dichroic mirror). (b) Energy-level diagram of $^{85}$Rb for three-color Rydberg excitation. (c)-(f) Experimental three-color Rydberg EIT signals for cells without inert gas, and with Ar, Ne, and N$_2$, respectively. Vertical scales are identical. In (d)-(f), the nominal pressure of the respective inert gases is 50 mTorr.
• Figure 2: Three-color Rydberg-EIT signals at 50 mTorr (top row) and 500 mTorr (bottom row) of (a)-(b) Ar, (c)-(d) Ne, and (e)-(f) N$_2$ inert gas in the cells. The $\Delta_C$- and $y$-scales are the same in all plots.
• Figure 3: Rydberg EIT with the RF-coupled triplet of states, $25F_{5/2}$, $25H_{9/2}$, and $25I_{11/2}$ (left column) and with the $50F_{5/2}$ state (right column), without and with the 453-nm light shone onto the cell walls. Top row - inert-gas-free cell, bottom row - cell with 50 mTorr of Ar. EIT peaks obtained from the inert-gas-free cell with the 453-nm light and the RF dressing fields turned off were used to mark the location $\Delta_C = 0$.