Multiorbital tunneling ionization of the CO molecule.
TL;DR: The results confirm that the shape of the ionizing orbitals determine the strong laser field tunneling ionization in the CO molecule, whereas the linear Stark effect plays a minor role.
Abstract: We coincidently measure the molecular-frame photoelectron angular distribution and the ion sum-momentum distribution of single and double ionization of CO molecules by using circularly and elliptically polarized femtosecond laser pulses, respectively. The orientation dependent ionization rates for various kinetic energy releases allow us to individually identify the ionizations of multiple orbitals, ranging from the highest occupied to the next two lower-lying molecular orbitals for various channels observed in our experiments. Not only the emission of a single electron, but also the sequential tunneling dynamics of two electrons from multiple orbitals are traced step by step. Our results confirm that the shape of the ionizing orbitals determine the strong laser field tunneling ionization in the CO molecule, whereas the linear Stark effect plays a minor role.
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TL;DR: The results reveal that efficient couplings between the ground and excited states of tunnel-ionized nitrogen molecules at various driver wavelengths in the near- and midinfrared range occur in strong laser fields, providing insight into the mechanism of free-space nitrogen ion lasers generated in remote air with strong femtosecond laser pulses.
Abstract: We carry out a combined theoretical and experimental investigation on the population distributions in the ground and excited states of tunnel-ionized nitrogen molecules at various driver wavelengths in the near- and midinfrared range. Our results reveal that efficient couplings (i.e., population exchanges) between the ground ${\mathrm{N}}_{2}^{+}({X}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+})$ state and the excited ${\mathrm{N}}_{2}^{+}({A}^{2}{\mathrm{\ensuremath{\Pi}}}_{u})$ and ${\mathrm{N}}_{2}^{+}({B}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+})$ states occur in strong laser fields. The couplings result in a population inversion between the ${\mathrm{N}}_{2}^{+}({X}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+})$ and ${\mathrm{N}}_{2}^{+}({B}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+})$ states at wavelengths near 800 nm, which is verified by our experimental observation of the amplification of a seed at $\ensuremath{\sim}391\text{ }\text{ }\mathrm{nm}$. The result provides insight into the mechanism of free-space nitrogen ion lasers generated in remote air with strong femtosecond laser pulses.
137 citations
TL;DR: This work probes the two-site double ionization of ArXe, where the instantaneous field direction at the moment of electron release and the emission direction of the correlated ionizing centre are measured by detecting the recoil sum- and relative-momenta of the fragment ions.
Abstract: Molecules in intense laser fields have enhanced multiple ionization rates, caused by the ionic core and laser fields acting on the part of the molecule in the up-field. Here, direct proof of this model is presented by studying the instantaneous effect of the field direction during double ionization in ArXe.
76 citations
TL;DR: This work analyzes a full, numerically exact many-body solution of the Schrödinger equation of a one-dimensional system with repulsive interactions tunneling to open space and shows how the emitted particles dissociate or fragment from the trapped and coherent source of bosons.
Abstract: The tunneling process in a many-body system is a phenomenon which lies at the very heart of quantum mechanics. It appears in nature in the form of α-decay, fusion and fission in nuclear physics, and photoassociation and photodissociation in biology and chemistry. A detailed theoretical description of the decay process in these systems is a very cumbersome problem, either because of very complicated or even unknown interparticle interactions or due to a large number of constituent particles. In this work, we theoretically study the phenomenon of quantum many-body tunneling in a transparent and controllable physical system, an ultracold atomic gas. We analyze a full, numerically exact many-body solution of the Schrodinger equation of a one-dimensional system with repulsive interactions tunneling to open space. We show how the emitted particles dissociate or fragment from the trapped and coherent source of bosons: The overall many-particle decay process is a quantum interference of single-particle tunneling processes emerging from sources with different particle numbers taking place simultaneously. The close relation to atom lasers and ionization processes allows us to unveil the great relevance of many-body correlations between the emitted and trapped fractions of the wave function in the respective processes.
65 citations
TL;DR: In this article, a review of recent advances made in studies of Coulomb explosion imaging, highlighting the use of this process to determine the static structures of complex molecules, geometric isomers, chiral molecules and molecular complexes.
Abstract: Intense femtosecond lasers as well as X-ray free electron lasers provide new means to produce multiply charged molecular cations. The fragmentation processes that these high energy species undergo, termed Coulomb explosion, are utilized to determine the static molecular structures as well as to trace the molecular dynamics of ultrafast chemical reactions. This review focuses on recent advances made in studies of Coulomb explosion imaging, highlighting the use of this process to determine the static structures of complex molecules, geometric isomers, chiral molecules and molecular complexes. Briefly, we summarize the recent time-resolved studies of surface electric fields and the controversy pertaining to the contribution of Coulomb explosion to the mechanism for ablation of solid surfaces.
59 citations
TL;DR: In this article, a grid-based numerical Hartree-fock approximation of the structure factor for the highest occupied molecular orbital (HOMO) is presented. But, for larger molecules, to solve the Hartreefock equations one should resort to basis-based approaches with too rapidly decaying Gaussian basis functions.
Abstract: Within the weak-field asymptotic theory, the dependence of the tunneling ionization rate of a molecule in a static electric field on its orientation with respect to the field is determined by the structure factor for the highest occupied molecular orbital (HOMO). An accurate determination of this factor, and hence the ionization rate, requires accurate values of the HOMO in the asymptotic region. Techniques for calculating the structure factors for molecules in the Hartree-Fock approximation are discussed. For diatomics, grid-based numerical Hartree-Fock calculations which reproduce the correct asymptotic tail of the HOMO are possible. However, for larger molecules, to solve the Hartree-Fock equations one should resort to basis-based approaches with too rapidly decaying Gaussian basis functions. A systematic study of the possibility to reproduce the asymptotic tail of the HOMO in calculations with Gaussian basis sets is presented. We find that polarization-consistent basis sets with quadruple or pentuple-zeta quality greatly improve the tail of the HOMO, but only when used with variationally optimized exponents. This methodology is validated by considering the CO molecule for which reliable grid-based calculations can be performed. The optimized Gaussian basis sets are used to calculate the structure factors for the triatomic molecules CO${}_{2}$ and OCS. The results are compared with available experimental and theoretical results.
54 citations