Department of Physics
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Item Interference Effect in the Relativistic Inner Shell Ionization of Atoms by Electron Impact(JSPF, 2006) Choubisa, RakeshWe present in this paper, the results of our calculation of right-left asymmetry in the relativistic (e, 2e) processes for inner K-shell ionization of atoms. The calculation has been performed in plane wave Born approximation (PWBA) using one photon exchange approximation. The triple differential cross section (TDCS), in plane wave Born approximation (PWBA) can be factorized into products of electron kinematic factors and atomic structure functions [Donnely (1984)]. The right left asymmetry in the relativistic (e, 2e) process on the K-shell of the atoms has been shown to depend on the interference between the transition charge and component of the transition current in the scattering plane. Further, we discuss the dependence of right-left asymmetry on the incident electron energy, atomic number of the target and scattering angle.Item On the effects of Orbital Angular Momentum (OAM) and impact parameters on (e, 2e) process on atoms by twisted electron(IOP, 2017) Choubisa, RakeshWe present our theoretical study of (e, 2e) process on atoms by the twisted electron, with special emphasis given on the effects of OAM and impact parameters on TDCS.Item Revisit of (e,2e) & (e,3e) processes on atoms with twisted electron impact(IOP, 2020) Choubisa, RakeshWe compute Triple Differential Cross Section (TDCS) and Five-fold Differential Cross Section (FDCS) for (e,2e) & (e,3e) processes on atoms respectively to investigate the effects of non zero angular momentum and the apex angle of the twisted electron. We observed that the differential coincidence cross sections largely depend on these parameters.Item Laser-assisted (e,2e) study with twisted electron beam on H-atom(ARXIV, 2023-08) Choubisa, RakeshWe study the laser-assisted twisted electron beam impact ionization of the hydrogen atom in coplanar asymmetric geometry. We develope the theoretical model in the first Born approximation. In the presence of the laser field, we treat the incident and scattered electrons as Volkov waves, the ejected electron, moving in the combined field of the laser and residual ion H + , is described by a Coulomb-Volkov wave function . In this communication, we compare the angular profile of triple differential cross-section (TDCS) for laser-assisted twisted electron beam incidence with the plane-wave, laser-assisted plane wave, and field-free twisted electron beam for (e,2e) processes, for different orbital angular momentum (OAM) number (m l ) values. We analyze the influence of the laser parameters (photon exchanged, intensity ) on the angular distribution of the TDCS. We study the (T DCS) av for macroscopic target to examine the effect of opening angle {\theta} p of the twisted electron beam on the angular profile of TDCS. Our results clearly show the impact of laser parameters (electric field ? and number of photon exchanged (l)) and twisted electron beam parameters (OAM number (m l ) and opening angle ({\theta} p )) on the angular distribution of TDCS.Item Twisted electron impact single ionization coincidence cross-sections for noble gas atoms(IOP, 2022-07) Choubisa, RakeshWe present the angular profiles of the triple differential cross-section (TDCS) for the (e, 2e) process on the noble gas atoms, namely He (1s), Ne (2s and 2p), and Ar (3p), for the plane wave and the twisted electron impact. We develop the theoretical formalism in the first Born approximation (FBA). The present study compares the TDCS for different values of orbital angular momentum number m and opening angles θp of the twisted electron beam with that of the plane wave beam in co-planar asymmetric geometry. In addition, we also investigate the TDCS for macroscopic targets to explore the influence of the opening angle θp of the twisted electron beam on the TDCS. Our results show that the peaks in binary and recoil regions shift from the momentum transfer direction. The results also show that for larger opening angles, the peaks for p-type orbitals split into double-peak structures, which are not observed in the plane wave results for the given kinematics. The angular profiles for averaged cross-section show the dependence of TDCS on the opening angles, especially for the larger opening angles, which are significantly different from the plane wave TDCS.Item Dynamics of Twisted Electron Impact Ionization of CH4 and NH3 Molecule(MDPI, 2023-05) Choubisa, RakeshElectron vortex beams (EVBs, also known as twisted electron beams) possess an intrinsic orbital angular momentum (OAM) with respect to their propagation direction. This intrinsic OAM represents a new degree of freedom that provides new insights into investigating the dynamics of electron impact ionization. In this communication, we present, in the first Born approximation (FBA), the angular profiles of the triple differential cross section (TDCS) for the (e, 2e) process on CH4 and NH3 molecular targets in the coplanar asymmetric geometry. We compare the TDCS of the EVB for different values of OAM number m with that of the plane wave. For a more realistic scenario, we investigate the average TDCS for macroscopic targets to explore the influence of the opening angle 𝜃𝑝 of the twisted electron beam on the TDCS. In addition, we also present the TDCS for the coherent superposition of two EVBs. The results demonstrate that the twisted (e, 2e) process retrieves the p-type character of the molecular orbitals, which is absent in the plane wave TDCS for the given kinematics. The results for the coherent superposition of two Bessel beams show the sensitivity of TDCS toward the OAM number m.Item Triple-differential cross section for the twisted-electron-impact ionization of the water molecule(APS, 2022-06) Choubisa, RakeshIn this paper, we present the results of the triple differential cross section (TDCS) for the (e, 2e) process on H2O molecule for the plane wave and the twisted electron beam impact. The formalism is developed in the first Born approximation. We describe the plane or twisted wave, plane wave, the linear combination of atomic orbitals (LCAO) (self-consistent field LCAO method), and Coulomb wave for the incident electron, scattered electron, the molecular state of H2O, and the ejected electron, respectively. We investigate the angular profiles of the TDCS for the outer orbitals 1b1, 3a1, 1b2, and 2a1 of the water molecule. We compare the angular profiles of the TDCS for the different values of orbital angular momentum (OAM) number m of the twisted electron beam with that of the plane wave beam. We also study the TDCS for macroscopic H2O target to explore the effect of opening angle θp of the twisted electron beam on the TDCS. Our results clearly show the effect of the twisted electron's OAM number (m) and the opening angle θp on the TDCS of the water molecule.Item Spin Asymmetry in (e, 2e) Processes on Li, Be+, B+2 and C+3 Targets by Transversely Polarized Electrons(IOP, 2004) Choubisa, RakeshWe present in this communication the results of our calculation of triple differential cross section (TDCS) and spin asymmetry in TDCS in (e, 2e) processes on Li, Be+, B+2 and C+3 targets at an incident electron energy 49 eV above the ionization potential for equal as well as unequal energy sharing conditions. We have performed the calculation in distorted wave Born approximation (DWBA) formalism using static exchange potential. We also present our calculation of spin asymmetry for Li like targets as a function of energy sharing ratio and compare it with the available experimental data for Li atom. We discuss the role of exchange effect in producing spin asymmetry. We observe that the triplet scattering process plays an important role as the nuclear charge is increased. Further we observe that the spin asymmetry variation with the energy sharing ratio is also sensitive to the nuclear chargeItem Electron impact single ionization of hydrogen molecule by twisted electron beam(IOP, 2020-12) Choubisa, RakeshIn this communication, we present the results of the five-fold differential cross-section (5DCS) and triple differential cross-section (TDCS) for the (e, 2e) process on molecular hydrogen (H2) by the plane wave and the twisted electron beam impact. The formalism is developed within the first Born approximation using the plane wave and the twisted wave for the incident electron beam. We describe the plane wave, Heitler–London type wave function, Coulomb wave for the scattered electron, the H2 molecular state, and the ejected electron. We compare the angular profiles of the 5DCS and TDCS for the different values of orbital angular momentum (OAM) number m of the twisted electron beam with that of the plane wave beam. We also present the 5DCS for different molecular orientations and study the effect of m on the 5DCS. We further investigate the influence of the twisted electron beam on the (e,2e) process on the H2 molecule from the perspective of the 'Young-type' interference of the scattered waves, emanating from the two atomic centers of the H2 molecule. We also study the TDCS for macroscopic H2 target to explore the effect of opening angle (θp) of the twisted electron beam on the TDCS. Our results clearly show the effect of the twisted electron's OAM number (m) and the opening angle (θp) on the 5DCS and TDCS of the molecular hydrogen.