STUDY OF TIME-DELAY FOUR-WAVE MIXING WITH INCOHERENT LIGHT IN ABSORPTION BANDS II: EXPERIMENT

Abstract

A series of experiments of time-delay four-wave mixing with incoherent light (TDFWM-IL) in absorption bands of ruby and dye molecules at 300 K-20 K are reported, which demonstrate that two-level theory fails in the interpretation of the results, and that our multilevel theory of TDFWM-IL should be applied. The following experimental results are emphasized: the normalized delay-time dependences of the signal intensity IS (τ) are not dependent on the sample temperature from 80 K to 300 K for the pump-beam wavelengths not closed to the zero-phonon line or the absorption edge as the power spectrum S0(ω) of the incoherent light source kept invariable; at low temperature of 20 K, IS(τ) is modulated periodically with a period equal to the interval of two adjacent vibrational transitions in the absorption band 4T2 of ruby, as predicted by the multilevel theory. The experiments performed at the zero-phonon line of ruby and at the absorption edge of Cresyl Violet in PMMA demonstrate that the effective two-level model is suitable to approximately analyze not only the experimental results of TDFWM-IL in the unresolved continuous absorption bands with homogeneous broadening, but also the effects of inhomogeneous broadening on the behavior of TDFWM-IL in these bands. Additionally, some data of the subpicosecond dephasing processes of these materials are also obtained for the first time.