The probe absorption spectrum measured in a two-level atomic system with two coupling fields. The frequency of the second coupling field is red-shifted with respect to the energy position of the gain peak formed only by the first coupling field. The peaks labeled as , , and (G, D, and A) represent the spectroscopic properties resulting from the transition connecting one pair of doubly dressed levels. The thick curve is the probe absorption spectrum in the presence of two coupling fields. The detunings of the two coupling fields are −12 MHz and −63 MHz with respect to the transition , respectively. The second coupling field is a counterpropagating beam acting on the atom sample. The medium thickness curve is the pump–probe spectrum measured in the presence of the first coupling field. The first coupling field is provided by the cooling/trapping beams with the detuning of −12 MHz with respect to the transition . The thin curve is the pump–probe spectrum measured in the presence of the second coupling field. In this case, the cooling/trapping beams are switched off and the second coupling field is provided by an independent frequency-stabilized diode laser. The detuning of the coupling field is −63 MHz with respect to the transition .