(color online) Probe gain spectra versus probe detuning with the same reduced Rabi frequencies and . (a) Red-dashed, black-short-dotted, and blue-solid lines represent MHz, 1.0 MHz, and 0.5 MHz, respectively. (b) Red-dashed, blue-solid, and black-short-dotted lines represent and , , and , MHz, and , respectively. Other parameters are the same as those in Fig. 3.