Figure 1

(a) FWM coupling scheme of the four-level ${}^{87}\mathrm{Rb}$ atoms. ${\Gamma }_3\left({\Gamma }_4\right)$ is the spontaneous decay rate $({\Gamma }_3\approx {\Gamma }_4=2\pi \times 5.4\times {10}^6{\mathrm{s}}^{-1})$. (b) Simplified experimental set up. BS, beam splitter ($T=92\%$, $R=8\%$); PBS, polarizing beam splitter; $D$, photodetector.Reuse & Permissions

Figure 2

(a) Calculated probe response vs the probe frequency detuning in the four-level EIT system (all other lasers are on resonance). (b) Calculated signal response vs the signal frequency detuning in the four-level EIT system (all other lasers are on resonance). The parameters are ${\Omega }_c=1.8{\Gamma }_3$, $\Omega =0.8{\Gamma }_3$, ${\Omega }_p=0.2{\Gamma }_3$, and ${\Omega }_s=0.02{\Gamma }_3$. For the absorption curves, values $>0(<0)$ indicate gain (absorption). Note that both the probe and the signal see the steep normal dispersion near their respective resonant frequencies, which results in slow group velocities for both the probe pulse and the generated signal pulse.Reuse & Permissions

Figure 3

(a) Measured (dots) and calculated (solid lines) probe transmission, and (b) measured (dots) and calculated (solid lines) FWM intensity (normalized relative to the probe intensity) vs the probe frequency detuning ${\Delta }_p$. The coupling laser and the pump laser are on resonance $({\Delta }_c=\Delta =0)$. ${\Omega }_c∕2\pi \approx 8\mathrm{MHz}$, ${\Omega }_p∕2\pi \approx 0.4\mathrm{MHz}$, and $\Omega ∕2\pi \approx 4\mathrm{MHz}$.Reuse & Permissions

Figure 4

(a) Measured probe transmission and (b) measured FWM intensity vs time for an incident probe pulse of $\sim 0.6\mu \mathrm{s}$ duration. In (a), top curve 1 is the reference probe pulse; curve 2 is the transmitted probe pulse with EIT only (without the pump laser); curve 3 is the transmitted probe pulse with the EIT modified by the pump laser. The dots are the experimental data and the solid lines are the Gaussian pulse fits. The scale is normalized relative to the reference probe. The experimental parameters are ${\Omega }_c∕2\pi \approx 9\mathrm{MHz}$, ${\Omega }_p∕2\pi \approx 0.4\mathrm{MHz}$, $\Omega ∕2\pi \approx 3\mathrm{MHz}$, and ${\Delta }_p={\Delta }_c=\Delta =0$.Reuse & Permissions

Figure 5

(a) The calculated group velocity of the probe light and (b) the FWM efficiency vs the coupling Rabi frequency ${\Omega }_c$. The dots (solid lines) are the experimental data (theoretical calculations). The experimental parameters are $\Omega ∕2\pi \approx 4\mathrm{MHz}$, ${\Omega }_p∕2\pi \approx 0.4\mathrm{MHz}$.Reuse & Permissions