Double-slit photoelectron interference in strong-field ionization of the neon dimer

Abstract

Wave-particle duality is an inherent peculiarity of the quantum world. The double-slit experiment has been frequently used for understanding different aspects of this fundamental concept. The occurrence of interference rests on the lack of which-way information and on the absence of decoherence mechanisms, which could scramble the wave fronts. Here, we report on the observation of two-center interference in the molecular-frame photoelectron momentum distribution upon ionization of the neon dimer by a strong laser field. Postselection of ions, which are measured in coincidence with electrons, allows choosing the symmetry of the residual ion, leading to observation of both, gerade and ungerade, types of interference.

Fig. 1

Two ionization pathways of neon dimer. a Relevant potential energy curves of the neutral and the singly charged neon dimer. Potential energy curves are taken from ref. . Spin-orbit splitting was simulated by separating the asymptotic parts of the I and II curves by 100 meV. b Kinetic energy release (KER) for the Ne⁺-Ne⁰ dissociation channel. Two dissociation pathways leading to Ne⁺-Ne⁰ fragmentation are shown by red (indirect) and blue (direct) arrows. The inset shows the electron momentum distribution in the molecular frame, when both pathways are considered. The red side of the sketched molecule defines the momentum direction of the detected neon ion. k_║ and k_⊥ are the electron momentum components parallel and perpendicular to the dimer axis, respectively. The corresponding orbitals of the neutral dimer are shown next to the potential energy curves. The ground state energy potential of the neutral dimer X¹∑_g⁺ as well as the corresponding probability distribution are shown for visualization of the ionization step according to the Franck-Condon principle

Fig. 2

Photoelectron momentum distributions of Ne₂ in the molecular frame for the circularly polarized light. a, d are simulated spectra with two coherently superimposed atomic distributions; b, e – measured for the direct and indirect dissociations, respectively; c, f are the same as the distributions in b, e but normalized to the monomer distribution in order to remove ionization weighting of the final momenta. The red side of the sketched molecule defines the momentum direction of the measured neon ion. k_║ and k_⊥ are the electron momentum components parallel and perpendicular to the dimer axis, respectively

Fig. 3

Photoelectron momentum distributions of Ne₂ for linearly polarized light. Normalized photoelectron momentum distributions projected to the molecular axis for the direct (a) and indirect (b) dissociation pathways in case of linearly polarized light. The spectra were generated by selecting only the events, where the dimer axis lies within ±15 to the polarization direction of the laser field. In addition, the ion momenta were limited to 4.5–16 a.u. and 39–45 a.u for the direct and indirect dissociation, respectively. Original spectra were divided by the corresponding spectrum of the monomer in order to remove the ionization weighting. k_║ is the electron momentum component parallel to the dimer axis

Fig. 4

Dependence of the two-center electron interference on the internuclear distance. The internuclear distance is encoded in the momentum of the ion. a, c – experimental distributions for the linearly polarized light (symmetrized with respect to the k_║ = 0 line) for direct and indirect dissociation pathways, respectively; b, d classical simulations using the II(1/2)_g and I(1/2)_u potential energy curves, respectively (Fig. 1). Each row in a, c was divided by the spectrum of the monomer in order to remove the ionization weighting. For the eye guidance, the white lines on the simulated distributions show dependence of the fringe position on the ion momentum. The dimer axis was selected to lie within ±15° to the field polarization direction. k_║ is the electron momentum component parallel to the dimer axis

Fig. 5

Comparison of the two methods in determination of the bond length. R_ion is the bond length of Ne₂ obtained from the ion momentum after the direct (blue) and indirect (red) fragmentations. R_interf is the bond length obtained from the corresponding two-center interference pattern. Statistical error bars for the R_interf correspond to the 1σ confidence interval. The black dashed diagonal line visualizes the exact matching dependence