Spatial distribution of H₂⁺ radiation harmonics in spatial homogeneous and inhomogeneous fields

In order to understand spatial distribution of H₂⁺ molecular harmonics, the spatial distribution of H₂⁺ molecular harmonic spectra in spatial homogeneous and inhomogeneous fields was studied through solving non-Bohn-Oppenheimer time-dependent Schr dinger equation. The results show that in spatial homogeneous field, harmonic intensity from positive-H nucleus is higher than that from negative-H nucleus. In spatial inhomogeneous field, due to plasma resonance on metallic nanostructure surface, harmonic cutoff is extended, and harmonic intensity from negative-H nucleus is higher than that from positive-H nucleus. Furthermore, spatial distribution of the harmonics can be explained by ionization probability, electron localization in two nuclei, time-dependent wave function and time-frequency analyses of harmonic spectra. Finally, by superposing a selected harmonics properly, an isolated ultrashort 36as pulse can be obtained. The investigation is helpful for understanding spatial distribution of molecular harmonics and producing attosecond pulses.