Multiresonance CARS spectra and excitation profiles of dye molecules in liquid solutions: 1,4-dihydroxy-anthraquinone in chloroform

The resonance CARS spectra and the excitation profile of the ground state vibrational mode at 460 cm-1 of 1,4-dihydroxy-anthraquinone in chlorofom solution at room temperature are reported. Experimental evidence has been obtained for the build up of excited state population during the CARS process and for the participation of higher (two-photon allowed) excited states to the resonance enhancement of excited state Raman bands and of the background signal. The third-order multiresonance CARS suscepbility is analysed theoretically for a six-level system including a two-photon allowed state and incoherent initial populations both in the ground and in the first excited state. The main features of the observed CARS spectra and excitation profile as well as the relation of the latter to the spontaneous Raman excitation profile are discussed on the basis of this model.