Figure 3
Density Plots of the D1 and D2 line. Density plots of the transparency features depending on the detunings of both lasers. The data is obtained by subtracting the background spectrum (coupling laser turned off) from the spectrum where the coupling laser is turned on (subtracting the two curves in Fig. 2 at each frequency of the coupling laser). Darker colors refer to high absorption and brighter colors refer to high transmission through the cell. The plots show the main transparency peaks moving along a straight line. The slope amounts to −2.08 ± 0.04 GHz819 nm/GHz589 nm. The observed transparencies beside the main peaks form anti crossings which are even observed at very far detuning of the coupling laser from the resonance point. Enhanced absorption (black areas) are also observed for far detunings of the lasers. In case of the sodium D2 line weak additional transparency features are observed, approximately +1.47 GHz apart from the main feature. The features are labeled in terms of their originating levels. The enhanced transparency and absorption values in percent are obtained by comparing the deviation of the transmission spectrum with the background spectrum (the two curves in Fig. 2), normalized by the maximum absorption of the background spectrum. For this recording the same probe and coupling laser powers as in Fig. 2 were used. Interestingly, the slope of the observed feature on the 32D3/2−level amounts to −1.53±0.08 GHz819 nm/GHz589 nm.
