Coherent control beyond population control and spectral interferences is demonstrated on the interferences and intensity of the two Autler-Townes ͑AT͒ components in the photoelectron spectrum of K atoms, using a sequence of two intense time-delayed femtosecond laser pulses. Photoelectron spectra were taken at various delay times between the two laser pulses and at different laser intensities at a fixed delay time. With respect to the interferences in the AT doublet the role of time delay and laser intensity is interchangeable for (n ϩ0.5) excitation. Strong laser fields or the optical phase of the delayed laser pulse allow the quantum mechanical phase of an atomic state to be manipulated in a symmetrical fashion. The observations are discussed in terms of a two-level model coupled to the continuum. For suitable combinations of the laser intensity of the first pulse and the time delay, the second laser pulse leaves the excited state population unchanged.

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Various one-parameter quantum control schemes applied to Na 2 serve as prototype for current multi-parameter control techniques in order to obtain physical insight into the underlying molecular dynamics.