arXiv subjects

Carlos Marante

Publications and source records attributed to Carlos Marante.

7 recordsLinked to original sources

arXiv2026

Femtosecond Nonadiabatic Confinement of Molecular Dication Yield

Doubly charged molecular cations often carry signatures of electronic correlation and electron-nuclear entanglement present in the parent cation. Here, we produce ethylene dications using a combination of an extreme ultraviolet pump and near-infrared probe pulses, observing a peak in the dication yield at a pump-probe delay of approximately 15 fs. Ab-initio calculations, which explicitly take into account coupled electron-nuclear dynamics induced by the pump and the multiphoton nature of the probe-induced ionization step, reproduced the observed delay in the yield. It originates from resonant enhancement of the multiphoton ionization of the electronically excited ethylene cation as the carbon-carbon double bond expands. However, this effect is tempered by rapid nonadiabatic relaxation of the excited ionic states. Our results suggest a general mechanism whereby ultrafast nonadiabatic relaxation of a molecular ion can compete with its strong-field ionization rate, confining the dication yield to a narrow temporal window of a few femtoseconds.

physics.chem-ph↗

arXiv2024

The influence of final state interactions in attosecond photoelectron interferometry

Fano resonances are ubiquitous phenomena appearing in many fields of physics, e.g. atomic or molecular photoionization, or electron transport in quantum dots. Recently, attosecond interferometric techniques have been used to measure the amplitude and phase of photoelectron wavepackets close to Fano resonances in argon and helium, allowing for the retrieval of the temporal dynamics of the photoionization process. In this work, we study the photoionization of argon atoms close to the $3s^13p^64p$ autoionizing state using an interferometric technique with high spectral resolution. The phase shows a monotonic $2{\pi}$ increase across the resonance or a sigmo\"idal less than ${\pi}$ variation depending on experimental conditions, e.g. the probe laser bandwidth. Using three different, state-of-the-art calculations, we show that the measured phase is influenced by the interaction between final states reached by two-photon transitions.

physics.atom-ph↗

arXiv2023

Two-electron interference in two-photon attosecond double ionization of neon

The pump-probe experiments enabled by X-ray free-electron lasers (XFEL) will allow us to directly observe correlated electronic motion with attosecond time resolution by detecting photoelectron pairs in coincidence. In helium, the transition between the non-sequential and sequential regime in two-photon double ionization (TPDI) is well explained by a virtual-sequential model. Much less is known, however, about the TPDI process in more complex atoms. Recently, we extended the virtual-sequential model to arbitrary light pulses [Chattopadhyay {\it et al.,} Phys. Rev. A~{\bf 108}, 013114 (2023)]. This extension employs multi-channel scattering states for the single ionization of both the neutral and the ionized target, which we initally applied to helium. In the present study, we show that our extended virtual-sequential model reproduces the qualitative features of the angularly integrated observables with available experimental results for neon, a considerably more complex target. We observe an intriguing feature of inverted two-particle interference in the joint energy distribution of $\mathrm{Ne}$ compared to $\mathrm{He}$. This phenomenon, attributable to the presence of a final doubly ionized state with triplet symmetry coupled to the two photoelectrons, should be observable with current experimental technologies.

physics.atom-ph↗

arXiv2023

ASTRA: a Transition-Density-Matrix Approach to Molecular Ionization

We describe \ASTRA{} (AttoSecond TRAnsitions), a new close-coupling approach to molecular ionization that uses many-body transition density matrices between ionic states with arbitrary spin and symmetry, in combination with hybrid integrals between Gaussian and numerical orbitals, to efficiently evaluate photoionization observables. Within the transition-density-matrix approach, the evaluation of inter-channel coupling is exact and does not depend on the size of the configuration-interaction space of the ions. Thanks to these two crucial features, \ASTRA{} opens the way to studying highly correlated and comparatively large targets at a manageable computational cost. Here, \ASTRA{} is used to predict the parameters of bound and autoionizing states of the boron atom and of the N$_2$ molecule, as well as the total photoionization cross section of boron, N$_2$, and formaldehyde, H$_2$CO. Our results are in excellent agreement with theoretical and experimental values from the literature.

physics.atom-ph↗

arXiv2023

Two-photon double ionization with finite pulses: Application of the virtual sequential model to helium

As a step toward the full \emph{ab-initio} description of two-photon double ionization processes, we present a finite-pulse version of the virtual-sequential model for polyelectronic atoms. The model relies on the \emph{ab initio} description of the single ionization scattering states of both the neutral and ionized target system. As a proof of principle and a benchmark, the model is applied to the helium atom using the {\tt NewStock} atomic photoionization code. The results of angularly integrated observables, which are in excellent agreement with existing TDSE (time-dependent Schr\"odinger equation) simulations, show how the model is able to capture the role of electron correlation in the non-sequential regime, and the influence of autoionizing states in the sequential regime, at a comparatively modest computational cost. The model also reproduces the two-particle interference with ultrashort pulses, which is within reach of current experimental technologies. Furthermore, the model shows the modulation of the joint energy distribution in the vicinity of autoionizing states, which can be probed with extreme-ultraviolet pulses of duration much longer than the characteristic lifetime of the resonance. The formalism discussed here applies also to polyelectronic atoms and molecules, thus opening a window on non-sequential and sequential double ionization in these more complex systems.

physics.atom-ph↗

arXiv2022

Measuring autoionization decay lifetimes of optically forbidden inner valence excited states in neon atoms with attosecond noncollinear four wave mixing spectroscopy

Attosecond noncollinear four wave mixing spectroscopy with one attosecond extreme ultraviolet (XUV) pulse and two few-cycle near-infrared (NIR) pulses was used to measure the autoionization decay lifetimes of inner valence electronic excitations in neon atoms. After a 43-48 eV XUV photon excites a 2s electron into the 2s2p6[np] Rydberg series, broadband NIR pulses couple the 2s2p6[3p] XUV-bright state to neighboring 2s2p6[3s] and 2s2p6[3d] XUV-dark states. Controllable delays of one or both NIR pulses with respect to the attosecond XUV pulse reveal the temporal evolution of either the dark or bright states, respectively. Experimental lifetimes for the 3s, 3p, and 3d states are measured to be 7 +/- 2 fs, 48 +/- 8 fs, and 427 +/- 40 fs, respectively, with 95% confidence. Accompanying calculations with two independent ab initio theoretical methods, NewStock and ASTRA, verify the findings. The results support the expected trend that the autoionization lifetime should be longer for states that have a smaller penetration in the radial region of the 2s core hole, which in this case is for the higher angular momentum Rydberg orbitals. The underlying theory thus links the lifetime results to electron correlation and provides an assessment of the direct and exchange terms in the autoionization process.

physics.atom-ph↗

arXiv2022

ASTRA, A Transition Density Matrix Approach to the Interaction of Attosecond Radiation with Atoms and Molecules

A new formalism and computer code, ASTRA (AttoSecond TRAnsitions), has been developed to treat the interactions of short, intense radiation with molecules. The formalism makes extensive use of transition density matrices, computed using a state-of-the-art quantum chemistry code (LUCIA), to efficiently calculate the many-body inter-channel-coupling interactions required to simulate the highly correlated electron dynamics due to atoms and molecules exposed to attosecond laser radiation.

physics.atom-ph↗