Role of the coupling laser in electromagnetically induced absorption

The cesium $D_2$ line closed hyperfine transition $F=4\to F^{\prime }=5$ was simultaneously coupled and probed in a hot atomic beam. We experimentally showed that, when the probe laser frequency approached that of the two-photon-resonance corresponding to electromagnetically induced absorption conditions, an enhanced transparency of the coupling laser appeared, combined with a further central absorption peak at zero probe laser detuning. Simultaneously, the coupling laser parametric dispersion showed a broad negative pattern together with a narrower steep positive phase shift in correspondence with the two-photon resonance, with sub-Doppler half-widths down to about $10\mathrm{kHz}$.

Figure 1

Level schematic of the $D_2$ line of atomic Cs. The $F$ levels are the hyperfine levels of the ground level $6s^2{S}_{1∕2}$. The $F^{\prime }$ are the hyperfine levels of the excited level $6p^2{P}_{3∕2}$. ${\gamma }_{54}$, spontaneous emission rates; ${\Omega }_{54}$, Rabi frequencies for the considered transition.

Figure 2

(Color online) Experimental setup. Cpl., Ref., Prb.: coupling, reference, and probe laser; P(45°): polarizer under 45° with respect to incident polarization; WP: Wollastone prism; PD: photodiode; LO: local oscillator; PLL: optical phase-locked loop; DBM: double balanced mixer; BS: power beam splitter; FMS: frequency modulation spectroscopy.

Figure 3

Coupling laser absorption coefficient for probe laser powers of $2.60\mathrm{mW}$, $0.71\mathrm{mW}$, $0.27\mathrm{mW}$, $69\mu \mathrm{W}$, and $41\mu \mathrm{W}$, respectively and a constant coupling laser power of $0.17\mathrm{mW}$.

Figure 4

Typical coupling laser absorption coefficient (above) and phase shift (below) corresponding to a probe laser EIA transition. The coupling and probe laser power are $0.16\mathrm{mW}$ and $0.25\mathrm{mW}$ (above) and $16\mu \mathrm{W}$ and $0.16\mathrm{mW}$ (below).

Figure 5

Absolute values of the observed coupling field dispersion at $0.26\mathrm{mW}$ probe laser power. The curve simulates the system under comparable experimental conditions.

Figure 6

Absolute values of the observed coupling field dispersion at $0.16\mathrm{mW}$ coupling laser power. The curve simulates the system under comparable experimental conditions.

Figure 7

Linewidth of the coupling laser parametric dispersion as a function of the probe field power at a constant coupling power of $16\mu \mathrm{W}$. HWHM: half-width at half maximum.