arXiv subjects

Gabriela Buica

Publications and source records attributed to Gabriela Buica.

12 recordsLinked to original sources

arXiv2024

Terrestrial Very-Long-Baseline Atom Interferometry: Summary of the Second Workshop

This summary of the second Terrestrial Very-Long-Baseline Atom Interferometry (TVLBAI) Workshop provides a comprehensive overview of our meeting held in London in April 2024, building on the initial discussions during the inaugural workshop held at CERN in March 2023. Like the summary of the first workshop, this document records a critical milestone for the international atom interferometry community. It documents our concerted efforts to evaluate progress, address emerging challenges, and refine strategic directions for future large-scale atom interferometry projects. Our commitment to collaboration is manifested by the integration of diverse expertise and the coordination of international resources, all aimed at advancing the frontiers of atom interferometry physics and technology, as set out in a Memorandum of Understanding signed by over 50 institutions.

hep-ex↗

arXiv2023

Circular dichroism in angular distribution of electron-hydrogen scattering in a two-color bicircular laser field

We study the origin of dichroic effects in elastic scattering of high energy electrons by hydrogen atoms in the presence of a two-color bicircular laser field of commensurate frequencies, in the domain of moderate intensities below 10 TW/cm2 . We use a semiperturbative approach in which the interaction of the hydrogen atom with the laser field is treated in second-order perturbation theory, while the interaction of the projectile electron with the laser field is described by Gordon- Volkov wave functions. An analytical formula of circular dichroism in the angular distribution of scattered electrons is derived in the weak-field domain for a two-color laser field that is a combination of the fundamental and its third harmonic. A comparison between the two-photon differential cross sections for two-color co- and counterrotating circularly polarized laser fields is made and the effect of the intensity ratio of the monochromatic field components on the circular dichroism is investigated. The dichroic effect in the angular distribution of scattered electrons for two-photon absorption is analyzed as a function of the scattering and azimuthal angles. We show that the two-color bicircular laser field can induce a strong circular dichroism in the angular distribution of scattered electrons at small scattering angles where the atomic dressing effects are important, as well at larger scattering angles. At small scattering angles we demonstrate that the dichroic effect for two-photon transitions can be predicted under the following conditions: the scattering process is treated in fist-order Born approximation and the dressing of the atomic states by the laser field is carried out at least in first-order time-dependent perturbation theory.

physics.atom-ph↗

arXiv2023

Laser-assisted inelastic electron scattering by excited hydrogen atoms

We theoretically study the inelastic electron-H($2s$) scattering in a linearly polarized laser field in the domain of high scattering energies and moderate field intensities. We investigate the angular distributions and the resonance structure of the differential scattering cross sections.

physics.atom-ph↗

arXiv2023

Symmetries in elastic scattering of electrons by hydrogen atoms in a two-color bicircular laser field

We consider the elastic scattering of electrons by hydrogen atoms in the presence of a two-color circularly polarized laser field in the domain of moderate intensities below $10^{13}$ W/cm$^2$ and high projectile energies. A hybrid approach is used, where for the interaction of the incident and scattered electrons with the laser field we employ the Gordon-Volkov wave functions, while the interaction of the hydrogen atom with the laser field is treated in second-order perturbation theory. Within this formalism, a closed analytical solution is derived for the nonlinear differential cross section, which is valid for circular as well linear polarizations. Simple analytical expressions of differential cross section are derived in the weak field domain for two-color laser field that is a combination of the fundamental and its second or third harmonics. It is shown that the nonlinear differential cross sections depend on the dynamical phase of the scattering process and on the helicities of the two-color circularly polarized laser field. A comparison between the two-photon absorption scattering signal for two-color co- and counter-rotating circularly polarized laser fields is made for even ($2ω$) or odd ($3ω$) harmonics, and the effect of the intensity ratio of the two-color laser field components is studied. We analyze the origin of the symmetries in the differential cross sections and we show that the modification of the photon helicity implies a change in the symmetries of the scattering signal.

physics.atom-ph↗

arXiv2023

Quantum interference effects in a $Λ$-type atom interacting with two short laser pulse trains

We study the quantum interference between the excitation pathways in a three-level $Λ$-type atom interacting with two short laser pulse trains under the conditions of electromagnetically induced transparency. The probability amplitude equations which describe the interaction of a three-level $Λ$-type atom with two laser pulse trains are numerically solved. We derive analytical expressions for the population of the upper excited state for resonant laser pulse trains with a rectangular temporal profile. By varying the parameters of the laser pulse trains such as area of a single pulse, detuning, repetition period, and number of individual pulses, we analyze the quantum interference between the excitation pathways in terms of the upper excited state population.

physics.atom-ph↗

arXiv2015

Inelastic scattering of electrons by metastable hydrogen atoms in a laser field

The inelastic scattering of fast electrons by metastable hydrogen atoms in the presence of a linearly polarized laser field is theoretically studied in the domain of moderate field intensities. The interaction of the hydrogen atom with the laser field is described by first-order time-dependent perturbation theory, while the projectile electrons interacting with the laser field are described by the Gordon-Volkov wave functions. An analytic expression is obtained for the differential scattering cross section in the first-order Born approximation for laser-assisted inelastic e-H(2s) scattering for the 2s-nl excitation. Detailed analytical and numerical results are presented for inelastic scattering accompanied by one-photon absorption, and the angular dependence and resonance structure of the differential cross sections is discussed for the 2s -4l excitation of metastable hydrogen.

physics.atom-ph↗

arXiv2014

Propagation of two short laser pulse trains in a $Λ$-type three-level medium under conditions of electromagnetically induced transparency

We investigate the dynamics of a pair of short laser pulse trains propagating in a medium consisting of three-level $Λ$-type atoms by numerically solving the Maxwell-Schrödinger equations for atoms and fields. By performing propagation calculations with different parameters, under conditions of electromagnetically induced transparency, we compare the propagation dynamics by a single pair of probe and coupling laser pulses and by probe and coupling laser pulse trains. We discuss the influence of the coupling pulse area, number of pulses, and detunings on the probe laser propagation and realization of electromagnetically induced transparency conditions, as well on the formation of a dark state.

physics.atom-ph↗

arXiv2013

Polarization Effects in Two-Photon Free-Free Transitions in Laser-Assisted Electron-Hydrogen Collisions

Two-photon free-free transitions in elastic laser-assisted electron-hydrogen collisions are studied in the domain of high scattering energies and low or moderate field intensities, in the third order of perturbation theory, taking into account all the involved Feynman diagrams. Based on the analytical expressions of the transition amplitudes, the differential cross sections for two-photon absorption/emission are computed at impact energy $E_i=100$ eV. The effect of field polarizations on the angular distribution and on the frequency dependence of the differential cross section is analyzed.

physics.atom-ph↗

arXiv2013

Two-, three-, and four-photon ionization of Mg in the circularly and linearly polarized laser fields: Comparative study using the Hartree-Fock and model potentials

We theoretically study multiphoton ionization of Mg in the circularly as well as the linearly polarized laser fields. Specifically two-, three-, and four-photon ionization cross sections from the ground and first excited states are calculated as a function of photon energy. Calculations are performed using the frozen-core Hartree-Fock and also the model potential approaches and the results are compared. We find that the model potential approach provide results as good as or even slightly better than those by the frozen-core Hartree-Fock approach. We also report the relative ratios of the ionization cross sections by the circularly and linearly polarized laser fields as a function of photon energy, which exhibit clear effects of electron correlations.

physics.atom-ph↗

arXiv2013

Effects of laser polarization on photoelectron angular distribution through laser-induced continuum structure

We theoretically investigate the effects of laser polarization on photoelectron angular distribution through laser-induced continuum structure. We focus on a polarization geometry where the probe and dressing lasers are both linearly polarized, and change the relative polarization angle between them. We find that the total ionization yield and the branching ratio into different ionization channels change as a function of the relative polarization angle, and accordingly the photoelectron angular distribution is altered. We present specific results for the $4p_{1/2}$-$6p_{1/2}$ and $4p_{3/2}$-$6p_{3/2}$ systems of the K atom, and show that the change of the polarization angle leads to the significant modification of photoelectron angular distribution.

physics.atom-ph↗

arXiv2013

Multiphoton ionization through the triplet states of Mg by linearly and circularly polarized laser pulses

We theoretically study multiphoton ionization through the triplet states of Mg by linearly polarized (LP) and circularly polarized (CP) fs laser pulses. After the construction of the atomic basis using the frozen-core Hartree-Fock potential (FCHFP) as well as the model potential (MP) approaches for both singlet and triplet series which show rather good agreements with the existing data in terms of state energies and dipole matrix elements, we solve time-dependent Schrödinger equations with $3s3p$ $^{3}P_{1}$ as an initial state, and calculate the total ionization yield and photoelectron energy spectra (PES).

physics.atom-ph↗

arXiv2013

Multiphoton ionization of the calcium atom by linearly and circularly polarized laser fields

We theoretically study multiphoton ionization of the Ca atom irradiated by the second (photon energy 3.1 eV) and third (photon energy 4.65 eV) harmonics of Ti:sapphire laser pulses (photon energy 1.55 eV). Because of the dense energy level structure the second and third harmonics of a Ti:sapphire laser are nearly single-photon resonant with the ${4s4p}$ $^1P^o$ and ${4s5p}$ $^1P^o$ states, respectively. Although two-photon ionization takes place through the near-resonant intermediate states with the same symmetry in both cases, it turns out that there are significant differences between them. The photoelectron energy spectra exhibit the absence/presence of substructures. More interestingly, the photoelectron angular distributions clearly show that the main contribution to the ionization processes by the third harmonic arises from the far off-resonant ${4s4p}$ $^1P^o$ state rather than the near-resonant ${4s5p}$ $^1P^o$ state. These findings can be attributed to the fact that the dipole moment for the ${4s^2}$ $^1S^e$ - ${4s5p}$ $^1P^o$ transition is much smaller than that for the ${4s^2}$ $^1S^e$ - ${4s4p}$ $^1P^o$ transition.

physics.atom-ph↗