THEORETICAL TREATMENT OF QUASI-BOUND RESONANCES IN 2-COLOR RESONANT 4-WAVE-MIXING SPECTROSCOPY

A treatment of continuum states in the application of diagrammatic per turbation theory to calculate the signal produced in two-color resonan t four-wave mixing (TC-RFWM) spectroscopy is developed. The third-orde r susceptibility is significantly modified from that obtained when con sidering only discrete states. To illustrate the contribution of conti nuum states, the line profile of a quasibound resonance arising from t he configuration interaction of bound and continuum states is derived. Analytic expressions for line profiles are presented for two specific experimental implementations of TC-RFWM used in gas-phase spectroscop ic studies. While the TC-RFWM line profiles are found to be very disti nct from the line profiles measured in linear spectroscopic techniques , the results demonstrate the important capability to characterize the TC-RFWM line profiles in terms of the same fundamental and physically significant parameters. [S1050-2947(98)01301-8].