Saturated absorption and electromagnetically induced transparency of residual rubidium in dense cesium vapor

Abstract

In the sealed-off cesium vapor cell studied in this work, a residual rubidium fraction of approximately $\sim$1\% was observed. We investigate the optical response of these trace Rb atoms in a sealed 1~cm long Cs-filled vapor cell. Despite the low concentration, laser excitation at 795~nm allows the observation of saturated absorption and electromagnetically induced transparency (EIT) resonances. The surrounding Cs vapor effectively acts as a buffer medium, reducing the Rb atomic velocity and increasing the interaction time with the laser field, which improves the EIT signal. The experiments are performed in an all-sapphire cell that can be heated up to 500$^{\circ}$C without window blackening, unlike conventional glass cells. From the measured spectra, Cs--Rb collisional cross sections are estimated. These results show that residual atomic species in high-temperature vapor cells can be exploited for spectroscopic and nonlinear-optical studies.

Figures (10)

• Figure 1: Laser-induced fluorescence spectrum recorded in the Cs-filled ASC under excitation at 852 nm. The dominant peak corresponds to the Cs $6P_{3/2}\rightarrow6S_{1/2}$ transition, while the weaker line at 795 nm originates from residual Rb atoms ($5P_{1/2}\rightarrow5S_{1/2}$). Inset: relevant Cs and Rb energy levels and their separation.
• Figure 2: Experimental arrangement used for spectroscopy at 795 nm. An external-cavity diode laser (ECDL) provides the radiation interacting with a $L=1$ cm all-sapphire cell containing Cs vapor with $\sim$1% residual Rb. M: mirror used to form counter-propagating beams, F: Filters, BS: Beam splitters, OS: Oscilloscope. The fluorescence spectrum from a Rb-filled nanocell is employed as a frequency reference.
• Figure 3: Curve 1 shows the Doppler-broadened transmission spectrum of 795 nm radiation through the ASC at a temperature of 190$^\circ$C. Curve 2 presents the reference fluorescence spectrum of the Rb nanocell. The inset shows the energy-level diagram and the studied transitions of the Rb $D_1$ line.
• Figure 4: Curve 1 shows the experimentally recorded SA-broadened transmission spectrum of 795 nm radiation through the ASC at a temperature of 190 $^{\circ}$C. Curve 2 shows the second-derivative (SD) spectrum of Curve 1 and is inverted for clarity. Curve 3 shows the reference spectrum. CO denotes the cross-over resonances appearing in saturated absorption spectra 141516.
• Figure 5: Dependence of the linewidth of the $^{87}$Rb $2 \rightarrow 2'$ transition on the 795 nm laser power. The inset shows a Gaussian fit of the VSOP resonance. The cell temperature is $T = 190~^{\circ}$C.