High-resolution Doppler spectroscopy of light-dressed states of multi-electron molecules

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In order to clarify the role of light-dressed states in the dynamics of a multielectron molecule in intense laser fields, the dissociation processes, O_2^+→O^++O, in intense laser fields (100fs, 〜3×10^<14> W/cm^2) are studied at the laser wavelength of 795 nm and 398 nm on the basis of the momentum imaging maps of the O^+ fragment ions. The covariance map measurements are performed with high momentum resolution to assign securely the dissociation pathways. From the anisotropic momentum distribution of O^+ with respect to the laser polarization direction, the electronic states of O_2^+ are found to be coupled exclusively through parallel transitions in the course of the dissociation process. The released kinetic-energy of O^+ for both 795 nm and 398 nm are interpreted consistently by a sequential coupling model of light-dressed potential curves of O_2^+ in the quartet Π- state manifold.The dispersed fluorescence spectra of NO and O_2 were measured in the spectral range between 300 nm and 700 nm using a spectrometer equipped with a intensified CCD camera. The observed spectra exhibits a number of spectral lines, most of which were assigned to the electronic transition of the higher charged fragment ions, such as N^+, N^<2+>, O^+ and O^<2+>. A high-resolution (〜2 cm^<-1> ) measurement was performed for the N III 3^2P°→3^2S transition at 409.24 nm. The observed spectra show a doublet pattern when the laser polarization is directed towards the spectrometer, which is interpreted as a result of a large released kinetic energy imposed on the N^<2+> fragment ion through the Coulomb explosion of NO.Based on the kinetic energy estimated from the split pattern of the spectra, it was found that the N^<2+> fragment was produced through the Coulomb explosion process, NO^<4+>→N^<2+>+O^<2+>.