Electron-nuclear correlated multiphoton-route to Rydberg fragments of molecules

Abstract

Atoms and molecules exposed to strong laser fields can be excited to the Rydberg states with very high principal quantum numbers and large orbitals. It allows acceleration of neutral particles, generate near-threshold harmonics, and reveal multiphoton Rabi oscillations and rich photoelectron spectra. However, the physical mechanism of Rydberg state excitation in strong laser fields is yet a puzzle. Here, we identify the electron-nuclear correlated multiphoton excitation as the general mechanism by coincidently measuring all charged and neutral fragments ejected from a H2 molecule. Ruled by the ac-Stark effect, the internuclear separation for resonant multiphoton excitation varies with the laser intensity. It alters the photon energy partition between the ejected electrons and nuclei and thus leads to distinct kinetic energy spectra of the nuclear fragments. The electron-nuclear correlation offers an alternative visual angle to capture rich ultrafast processes of complex molecules.

Laser-induced dissociative recombination of carbon dioxide

“…1(b). This observation contradicts a previous experimental observation of hydrogen [27], in which Rydberg states are formed via resonant multiphoton excitation by irradiation of the circularly polarized laser fields. Our observation confirms that in our work Rydberg states are formed through frustrated double ionization, which is a rescattering-like process [9,10,28].…”

Triple ionization and frustrated triple ionization in triatomic molecules driven by intense laser fields

“…This feature is most prevalent when 800-and 400-nm laser fields are employed with a field-strength ratio equal to two [24]. In addition, fingerprints of nuclear motion on the electron dynamics have been previously identified in frustrated double ionization [25,26]. Such a signature includes an oscillation in the principal n quantum number [25].…”

Enhancing frustrated double ionization with no electronic correlation in triatomic molecules using counter-rotating two-color circular laser fields

“…Rydberg states underlie, for instance, acceleration of neutral particles [1], spectral features of photoelectrons [2], formation of molecules via long-range interactions [3], and inversion of N 2 in free-space air lasing [4]. Recently, the formation of Rydberg states in weakly-driven H 2 was accounted for by electron-nuclear correlated multiphoton resonant excitation [5]. For H 2 driven by intense infrared laser fields (strongly-driven), this latter process was shown to merge with frustrated double ionization (FDI) [5].…”

“…We also fully account for the Coulomb singularities [15]. The motion of the electrons and the nuclei are treated on an equal footing, accounting for the interwind electron-nuclear dynamics [5,39]. During propagation, we allow each electron to tunnel with a quantum-mechanical probability given by the Wentzel-Kramers-Brillouin approximation [12,15].…”

“…Recently, the formation of Rydberg states in weakly-driven H 2 was accounted for by electron-nuclear correlated multiphoton resonant excitation [5]. For H 2 driven by intense infrared laser fields (strongly-driven), this latter process was shown to merge with frustrated double ionization (FDI) [5]. FDI accounts for the formation of Rydberg fragments in strongly-driven two-electron molecules.…”