  We consider pump-probe spectroscopy of a single ion with a highly metastable
(probe) clock transition which is monitored by using the quantum jump
technique. For a weak clock laser we obtain the well known Autler-Townes
splitting. For stronger powers of the clock laser we demonstrate the transition
to a new regime. The two regimes are distinguished by the transition of two
complex eigenvalues to purely imaginary ones which can be very different in
magnitude. The transition is controlled by the power of the clock laser. For
pump on resonance we present simple analytical expressions for various
linewidths and line positions.
