Agnieszka Jaron-Becker / Jaron | University of Colorado, Boulder (original) (raw)

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Papers by Agnieszka Jaron-Becker / Jaron

Physical Review A

A circularly polarized laser pulse can induce persistent intramolecular currents by either exciti... more A circularly polarized laser pulse can induce persistent intramolecular currents by either exciting or ionizing molecules. These two cases are identified as electron currents and hole currents, respectively, and up to now they have been studied only separately. We report ab initio time-dependent density-functional theory (TDDFT) simulations of currents in a molecule, which reveal for the first time that both electron and hole currents can be present simultaneously. By adjusting the intensity of the laser pulse, the balance between the two types of current can be controlled and the overall sign of the current can be switched. We provide a physical explanation for the effect in terms of molecular orbitals, which is consistent with the TDDFT simulations.

arXiv (Cornell University), 2023

A circularly polarized laser pulse can induce persistent intra-molecular currents by either excit... more A circularly polarized laser pulse can induce persistent intra-molecular currents by either exciting or ionizing molecules. These two cases are identified as electron currents and hole currents, respectively, and up to now they have been studied only separately. We report ab initio time-dependent density-functional theory (TDDFT) simulations of currents during resonance-enhanced two-photon ionization of benzene, which reveal for the first time that both electron and hole currents can be present simultaneously. By adjusting the intensity of the laser pulse, the balance between the two types of current can be controlled, and the overall sign of the current can be switched. We provide a physical explanation for the effect in terms of complex molecular orbitals which is consistent with the TDDFT simulations.

Proceedings of the 2022 International Symposium on Molecular Spectroscopy

Cornell University - arXiv, 2023

We study the ellipticity of high-order harmonics emitted from CO2 molecule driven by linearly pol... more We study the ellipticity of high-order harmonics emitted from CO2 molecule driven by linearly polarized laser fields using numerical simulations within the time-dependent density functional theory. We find that the overall ellipticity of the harmonics is small, which is in agreement with experimental data. On the other hand, our analysis of the numerical results indicates that several valence orbitals contribute significantly to the harmonic emission and some of these contributions show a strong ellipticity of the harmonics. The small ellipticity in the total harmonics signal arises from a combination of factors, namely, the fact that harmonic emission from different orbitals is strongest at different alignment angles of the molecular axis with respect to the laser polarization direction, as well as interference effects and a strong laser coupling between several inner valence orbitals.

Physical Review A, 1999

It is shown that the exchange of an odd number of photons in laser-assisted charge-particle scatt... more It is shown that the exchange of an odd number of photons in laser-assisted charge-particle scattering is forbidden when the laser polarization is perpendicular to the scattering plane. It is proposed that this selection rule may be used to test the satisfaction of single-collision conditions under critical geometrical conditions where experimental count rates tend to become prohibitively small.

Proceedings of the 74th International Symposium on Molecular Spectroscopy, 2019

$Research paper thumbnail of Role of central frequency in pulse shapes used in simulations of Time Dependent Schr\"{o}dinger Equation$

Bulletin of the American Physical Society, 2018

We experimentally demonstrate angularly and temporally isolated counter-rotating circularly polar... more We experimentally demonstrate angularly and temporally isolated counter-rotating circularly polarized attosecond pulses at 33 eV. The pulse contrast and circular polarization of the beams are fully characterized by a field autocorrelator and an EUV polarimeter.

We study ionization of molecules by an intense laser field over a broad wavelengthregime, ranging... more We study ionization of molecules by an intense laser field over a broad wavelengthregime, ranging from 0.8 to 1.5 μmexperimentally and from 0.6 to 10 μm theoretically. A reaction microscope is combined with an optical parametric amplifier to achieve ionization yields in the near-infrared wave- lengthregime.Calculationsaredoneusingthestrong-fieldS-matrixtheoryand agreementisfoundbetweenexperimentandtheory,showingthationizationof many molecules is suppressed compared to the ionization of atoms with identical ionization potentials at near-infrared wavelengths at around 0.8 μm, but not at longest wavelengths (10 μm). This is due to interference effects in the electron emission that are effective at low photoelectron energies but tend to average out at higher energies. We observe the transition between suppression and nonsuppression of molecular ionization in the near-infrared wavelength regime (1� 5 μm).

Physical Review A, Nov 9, 2017

We analyze the time-dependent nonlinear response of helium atom to a strong laser pulse in form o... more We analyze the time-dependent nonlinear response of helium atom to a strong laser pulse in form of the induced nonlinear electric susceptibility. Our theoretical predictions are based on ab-initio solutions of the time-dependent Schrödinger equation obtained using a numerical basis state method and the short-time Fourier transform. The results qualitatively reproduce features seen in recent experimental data. In particular, we observe deviations from the adiabatic (field-following) response in the electric susceptibility at high intensities. According to our analysis a shift of the peak towards the front of the pulse and changes in the concavity of the slope in the trailing edge of the pulse can be related to the population of continuum states and bound excited states with high angular quantum number during the interaction of the atom with the laser pulse.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2017

Physical Review A, 2018

We analyze the role of the difference between the central frequencies of the spectral distributio... more We analyze the role of the difference between the central frequencies of the spectral distributions of the vector potential and the electric field of a short laser pulse. The frequency shift arises when the electric field is determined as the derivative of the vector potential to ensure that both quantities vanish at the beginning and end of the pulse. We derive an analytical estimate of the frequency shift and show how it affects various light induced processes, such as excitation, ionization and high harmonic generation. Since observables depend on the frequency spectrum of the electric field, the shift should be taken into account when setting the central frequency of the vector potential to avoid potential misinterpretation of numerical results for processes induced by few-cycle pulses.

New Journal of Physics, 2016

Science (New York, N.Y.), Jan 4, 2015

High-harmonic generation is a universal response of matter to strong femtosecond laser fields, co... more High-harmonic generation is a universal response of matter to strong femtosecond laser fields, coherently upconverting light to much shorter wavelengths. Optimizing the conversion of laser light into soft x-rays typically demands a trade-off between two competing factors. Because of reduced quantum diffusion of the radiating electron wave function, the emission from each species is highest when a short-wavelength ultraviolet driving laser is used. However, phase matching--the constructive addition of x-ray waves from a large number of atoms--favors longer-wavelength mid-infrared lasers. We identified a regime of high-harmonic generation driven by 40-cycle ultraviolet lasers in waveguides that can generate bright beams in the soft x-ray region of the spectrum, up to photon energies of 280 electron volts. Surprisingly, the high ultraviolet refractive indices of both neutral atoms and ions enabled effective phase matching, even in a multiply ionized plasma. We observed harmonics with v...