Source: http://aoot.osa.org/josab/abstract.cfm?uri=josab-34-4-877
Timestamp: 2019-04-23 13:59:33+00:00

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Strong enhancement of group refractive index in a dense buffered atomic vapor is recorded using a technique of reflection from a low-finesse Fabry–Perot cavity filled with dense atomic vapor allowing the retrieval of a dispersion curve for the hyperfine structure of Rb D2 line buffered by a high-density Cs vapor. Oscillations of the recorded signal resulting from interference of beams reflected from the front and rear windows of the cell appearing with the laser frequency scanning across the resonance allow easy reconstruction of the dispersion curve. Contribution from concomitant interconnected processes, in particular, the determinative role of radiation channeling in enhancement of the resonator Q-factor, is analyzed.
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Fig. 1. Schematic drawing of the experimental setup (optical part).
Fig. 2. Reflection (upper trace) and transmission (middle trace) spectra in the region of D2 line of residual Rb vapor recorded at Tsa=269°C and Tw=440°C (NRb=2.02×1013 cm−3, NCs=1.30×1016 cm−3, NCs2=9.24×1012 cm−3), and room temperature Rb reference spectrum (lower trace). D2 line hyperfine transition groups Rb87 Fg=2→Fe=1,2,3, Rb85 Fg=3→Fe=2,3,4, Rb85 Fg=2→Fe=1,2,3, and Rb87 Fg=1→Fe=0,1,2 (left to right) are denoted by vertical lines.
Fig. 3. Dependence of group refractive index ng on frequency retrieved from experimental reflection spectra (dots) and calculated by Eqs. (4) and (11) (solid lines; see Section 3) in the region of D2 line of residual Rb vapor for four temperature regimes: (a) Tsa=220°C, Tw=350°C; (b) Tsa=260°C, Tw=370°C; (c) Tsa=300°C, Tw=400°C; (d) Tsa=350°C, Tw=410°C. The zero detuning frequency is set to the Fg=2→Fe=1 hyperfine transition of Rb87.
Fig. 4. Reflection (upper graph) and transmission (lower graph) spectra in the region of D2 line of Rb atoms calculated by Eq. (12) for the conditions in Fig. 2, with a fitting parameter of Γ¯=2π×23.3 MHz≈146.7 MHz. The zero detuning frequency is set to the Fg=2→Fe=1 hyperfine transition of Rb87D2 line.
Fig. 5. Frequency dependencies of the real (upper graph) and imaginary (middle graph) parts of refractive index calculated by Eq. (11) in the region of D2 line of Rb for the conditions in Fig. 2. The lower graph shows the corresponding group refractive index calculated by Eq. (4). The zero detuning frequency is set to the Fg=2→Fe=1 transition of Rb87.
Fig. 6. Buildup of channeled backward beam under non-normal incidence ϕ≠0, waveguided along a high-refractive-index laser beam. I, T, and R represent incident, transmitted, and geometrically reflected beams, respectively; intense color—overlapping area of forward and backward beams.

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