PROPAGATION EFFECTS IN 2-COLOR COHERENT-CONTROL PROCESSES

We have investigated a two-color coherent-control process at high dens ities of the absorbing medium. Irradiating a vapor of atomic mercury w ith a coherent field, with one component nearly resonant with the thre e-photon 6s S-1(0)-->6p P-1(1)o transition, and the other component th e third harmonic of the first, we observe the interference between the two excitation pathways for this transition. Measurements of this int eraction as the density of the mercury vapor is increased show evidenc e of nonlinear coupling (phase and amplitude locking) of the two field components with each other. This is manifested as a decrease in the m agnitude of the photoionization signal, as well as a decrease of the d epth of modulation of the photoionization signal.