Vibrationally resolved above-threshold ionization in NO molecules by intense ultrafast two-color laser pulses: An experimental and theoretical study

Abstract

We present above-threshold ionization (ATI) in the molecule nitric oxide, NO, by intense (${10}^{12}--{10}^{13}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$) two-color femtosecond laser pulses. Vibrationally resolved coherent interference phenomena of multiphoton and multipathway ionization processes have been investigated by measuring experimentally and modeling theoretically the molecular photoionization yields. We find that the ATI photoelectron distribution of NO, initiated from degenerate electronic and vibrational states, depends on the relative phase of the two pulses, the kinetic energy, and emission angle of the photoelectrons. This dependence codes the information of interference effects of molecular electronic states. AC Stark effects modulate interference patterns in ATI spectra. Moreover, the ATI spectra exhibit peak energy dependencies that illustrate interference effects from coherent couplings between various ionization channels. These features reflect the molecular property and the multiple channel ionization interference effects in ATI processes. The results allow to explore coherent electron-vibration processes in ultrafast molecular photoionization.