 The result of the AC field on the atom is thus to shift the strongly coupled bare atom energy eigenstates into two states formula_33 and formula_34 which are now separated by formula_37.Evidence of this shift is apparent in the atom's absorption spectrum, which shows two peaks around the bare transition frequency, separated by formula_29 (Autler-Townes splitting).The modified absorption spectrum can be obtained by a pump-probe experiment, wherein a strong "pump" laser drives the bare transition while a weaker "probe" laser sweeps for a second transition between a third atomic state and the dressed states.