arXiv subjects

Gábor J. Halász

Publications and source records attributed to Gábor J. Halász.

29 records · Page 2Linked to original sources

arXiv2019

Rovibronic spectra of molecules dressed by light fields

The theory of rovibronic spectroscopy of light-dressed molecules is presented within the framework of quantum mechanically treated molecules interacting with classical light fields. Numerical applications are demonstrated for the homonuclear diatomic molecule Na$_2$, for which the general formulae can be simplified considerably and the physical processes leading to the light-dressed spectra can be understood straightforwardly. The physical origin of different peaks in the light-dressed spectrum of Na$_2$ is given and the light-dressed spectrum is investigated in terms of its dependence on the dressing field's intensity and wavelength, the turn-on time of the dressing field, and the temperature. The important implications of light-dressed spectroscopy on deriving field-free spectroscopic quantities are also discussed.

physics.chem-ph↗

arXiv2019

Ultrafast dynamics in the vicinity of quantum light-induced conical intersections

Nonadiabatic effects appear due to avoided crossings or conical intersections that are either intrinsic properties in field-free space or induced by a classical laser field in a molecule. It was demonstrated that avoided crossings in diatomics can also be created in an optical cavity. Here, the quantized radiation field mixes the nuclear and electronic degrees of freedom creating hybrid field-matter states called polaritons. In the present theoretical study we go further and create conical intersections in diatomics by means of a radiation field in the framework of cavity quantum electrodynamics (QED). By treating all degrees of freedom, that is the rotational, vibrational, electronic and photonic degrees of freedom on an equal footing we can control the nonadiabatic quantum light-induced dynamics by means of conical intersections. First, the pronounced difference between the the quantum light-induced avoided crossing and the conical intersection with respect to the nonadiabatic dynamics of the molecule is demonstrated. Second, we discuss the similarities and differences between the classical and the quantum field description of the light for the studied scenario.

physics.chem-ph↗

arXiv2019

Robust field-dressed spectra of diatomics in an optical lattice

The absorption spectra of the cold Na2 molecule dressed by a linearly polarized standing laser wave is investigated. In the studied scenario the rotational motion of the molecules is frozen while the vibrational and translational degrees of freedom are accounted for as dynamical variables. In such a situation a light-induced conical intersection (LICI) can be formed. To measure the spectra a weak field is used whose propagation direction is perpendicular to the direction of the dressing field but has identical polarization direction. Although LICIs are present in our model, the simulations demonstrate a very robust absorption spectrum, which is insensitive to the intensity and the wavelength of the dressing field and which does not reflect clear signatures of light-induced nonadiabatic phenomena related to the strong mixing between the electronic, vibration and translational motions. However, by widening artificially the very narrow translational energy level gaps, the fingerprint of the LICI appears to some extent in the spectrum.

physics.chem-ph↗

arXiv2018

Conical Intersections Induced by Quantum Light: Field-Dressed Spectra from the Weak to the Ultrastrong Coupling Regimes

A fundamental theoretical framework is formulated for the investigation of rovibronic spectra resulting from the coupling of molecules to one mode of the radiation field in an optical cavity. The approach involves the computation of (1) cavity-field-dressed rovibronic states, which are hybrid light-matter eigenstates of the `molecule + cavity radiation field' system, and (2) the transition amplitudes between these field-dressed states with respect to a weak probe pulse. The predictions of the theory are shown for the homonuclear Na$_2$ molecule. The field-dressed rovibronic spectrum demonstrates undoubtedly that the Born--Oppenheimer approximation breaks down in the presence of the cavity radiation field. A clear fingerprint of the strong nonadiabaticity is found, which can only emerge in the close vicinity of conical intersections. In this work, the conical intersection is induced by the quantized radiation field, and it is thus called a "light-induced conical intersection" (LICI). Dependence of the cavity-field-dressed spectrum on the cavity-mode wavelength as well as on the light-matter coupling strength is investigated. Essential changes are identified in the spectra from the weak to the ultrastrong coupling regimes.

physics.atm-clus↗

arXiv2017

Geometric phase of light-induced conical intersections: Adiabatic time-dependent approach

Conical intersections are degeneracies between electronic states and are very common in nature. It has been found that they can also be created both by standing or by running laser waves. The latter are called light-induced conical intersections. It is well known that conical intersections are the sources for numerous topological effects which are manifested e.g. in the appearance of the geometric or Berry phase. In one of our former works by incorporating the diabatic-to-adiabatic transformation angle with the line-integral technique we have calculated the Berry-phase of the light-induced conical intersections. Here we demonstrate that by using the time dependent adiabatic approach suggested by Berry the geometric phase of the light-induced conical intersections can also be obtained and the results are very similar to those of the time-independent calculations.

physics.chem-ph↗

arXiv2016

Towards controlling the dissociation probability by light-induced conical intersections

Light-induced conical intersections (LICIs) can be formed both by standing or by running laser waves. The position of a LICI is determined by the laser frequency while the laser intensity controls the strength of the nonadiabatic coupling. Recently, it was shown within the LICI framework that linearly chirped laser pulses have an impact on the dissociation dynamics of the $D_{2}^{+}$ molecule (J. Chem. Phys. 143, 014305, (2015); ibid 144, 074309, (2016)). In this work we exploit this finding and perform calculations using chirped laser pulses in which the time dependence of the laser frequency is designed so as to force the LICI to move together with the field-free vibrational wave packet as much as possible. Since nonadiabaticity is strongest in the vicinity of the conical intersection, this is the first step towards controlling the dissociation process via the LICI. Our showcase example is again the $D_{2}^{+}$ molecular ion. To demonstrate the impact of the LICIs on the dynamical properties of diatomics, the total dissociation probabilities and the population of the different vibrational levels after the dissociation process are studied and discussed.

physics.atm-clus↗

arXiv2016

Tracking the photodissociation probability of D$_2^+$ induced by linearly chirped laser pulses

In the presence of linearly varying frequency chirped laser pulses the photodissociation dynamics of D$_2^+$ is studied theoretically after ionization of D$_{2}$ . As a completion of our recent work (J. Chem. Phys. 143, 014305 (2015)) a comprehensive dependence on the pulse duration and delay time is presented in terms of total dissociation probabilities. Our numerical analysis carried out in the recently introduced light-induced conical intersection (LICI) framework clearly shows the effects of the changing position of the LICI which is induced by the frequency modulation of the chirped laser pulses. This impact is presented for positively, negatively and zero chirped short pulses.

physics.atm-clus↗

arXiv2016

Towards the full quantum dynamical description of photon induced processes in $\mathrm{D}_{2}^{+}$

A new quantum dynamical model has been developed to describe the dissociative ionization of deuterium molecular ions by intense laser pulses ($τ=10$ fs, $λ=200$ nm and $I=3\times10^{13}$ W/cm$^{2}$). We calculated the ionization probability densities by solving the time-dependent Schrödinger equation numerically. Throughout the simulation the nuclear vibration was considered as a dynamic variable with fixed molecular axis orientation. Benchmark calculations were performed for the ionization of $\mathrm{HeH}^{++}$, for which accurate numerical results are available in the literature, in order to check the performance of this new restricted model.

physics.atm-clus↗

arXiv2014

Direct signature of light-induced conical intersections in diatomics

Nonadiabatic effects are ubiquitous in physics, chemistry and biology. They are strongly amplified by conical intersections (CIs) which are degeneracies between electronic states of triatomic or larger molecules. A few years ago it has been revealed that CIs in molecular systems can be formed by laser light even in diatomics. Due to the prevailing strong nonadiabatic couplings, the existence of such laser-induced conical intersections (LICIs) may considerably change the dynamical behavior of molecular systems. By analyzing the photodissociation process of the D2+ molecule carefully, we found a robust effect in the angular distribution of the photofragments which serves as a direct signature of the LICI providing undoubted evidence for its existence.

physics.atm-clus↗

arXiv2013

Nuclear wave packet quantum interference in the intense laser dissociation of the $\mathrm{D}_{2}^{+}$ molecule

Recently it has been recognized that electronic conical intersections in molecular systems can be induced by laser light even in diatomics. As is known a direct consequence of these accidental degeneracies is the appearence of nonadiabatic effects which has a strong impact on the nuclear quantum dynamics. Studying the photodissociation process of the $\mathrm{D}_{2}^{+}$ molecule, we report here some novel and observable quantum interference phenomena that arise from the topological singularity induced by a strong laser field.

physics.atm-clus↗

arXiv2013

Coherence revival during the attosecond electronic and nuclear quantum photodynamics of the ozone molecule

A coherent superposition of two electronic states of ozone (ground and Hartley B) is prepared with a UV pump pulse. Using the multiconfiguration time-dependent Hartree approach, we calculate the subsequent time evolution of the two corresponding nuclear wave packets and the coherence between them. The resulting wave packet shows an oscillation between the two chemical bonds. Even more interesting, the coherence between the two electronics states reappears after the laser pulse is switched off, which could be observed experimentally with an attosecond probe pulse.

physics.atm-clus↗