Beyond the dipole approximation: angular-distribution effects in valence photoemission

Hemmers, Oliver; Fisher, Galen B.; Glans, Peter; Hansen, D. L.; Wang, H; Whitfield, S. B.; Wehlitz, R.; Levin, J. C.; Sellin, I. A.; Perera, R. C. C.; Dias, E. W. B.; Chakraborty, Himadri; Deshmukh, P. C.; Manson, Steven T.; Lindle, Dennis W.

doi:10.1088/0953-4075/30/21/003

Cited by 101 publications

(56 citation statements)

References 24 publications

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“…These experiments were performed with synchrotron radiation from storage rings, thus due to the low intensity of the photon flux the probability of the second-step ionization (23) was negligible. Nevertheless, pronounced non-dipole effects in single ionization revealed in these experiments [36,37] point to potentially strong non-dipole effects in the 2PDI at the corresponding photon energies. Using the Free-electron LASer in Hamburg (FLASH), the angular distributions of the individual electrons e 1 and e 2 in the 2PDI process (22), (23) were measured in [15,22] while the angular correlation function between the two electrons was observed in [16].…”

Section: Sequential 2pdi Of Neonmentioning

confidence: 73%

Non-dipole effects in the angular distribution of photoelectrons in sequential two-photon atomic double ionization

Grum-Grzhimailo¹,

Грызлова²,

Meyer³

2012

J. Phys. B: At. Mol. Opt. Phys.

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Abstract. Motivated by the recent achievements of experiments using X-ray free electron lasers, we develop a theory for the angular distributions of photoelectrons in sequential two-photon double ionization (2PDI) of atoms beyond the dipole approximation. Expressions for the angular distributions are obtained taking into account the full multipole expansion of radiation in electric and magnetic moments. The formalism is further specified for the first-order corrections to the dipole approximation. As illustrative example, the sequential 2PDI of the 2p shell in atomic neon is studied. The numerical calculations predict distinct non-dipole effects observable in experiments at present X-ray Free Electron Lasers.

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Section: Sequential 2pdi Of Neonmentioning

confidence: 73%

Non-dipole effects in the angular distribution of photoelectrons in sequential two-photon atomic double ionization

Grum-Grzhimailo¹,

Грызлова²,

Meyer³

2012

J. Phys. B: At. Mol. Opt. Phys.

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“…One application of this atomic Auger Doppler effect is the determination of unknown angular distributions for high-energy photoelectrons. Because of the difficulty to detect such electrons, these angular distributions are rarely measured at energies high above threshold (see for example, Ne 2p up to 1,200 eV above threshold 26 ). At these high energies, non-dipole effects are expected to occur.…”

Section: Resultsmentioning

confidence: 99%

Atomic Auger Doppler effects upon emission of fast photoelectrons

et al. 2014

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Studies of photoemission processes induced by hard X-rays including production of energetic electrons have become feasible due to recent substantial improvement of instrumentation. Novel dynamical phenomena have become possible to investigate in this new regime. Here we show a significant change in Auger emission following 1s photoionization of neon, which we attribute to the recoil of the Ne ion induced by the emission of a fast photoelectron. Because of the preferential motion of the ionized Ne atoms along two opposite directions, an Auger Doppler shift is revealed, which manifests itself as a gradual broadening and doubling of the Auger spectral features. This Auger Doppler effect should be a general phenomenon in high-energy photoemission of both isolated atoms and molecules, which will have to be taken into account in studies of other recoil effects such as vibrational or rotational recoil in molecules, and may also have consequences in measurements in solids.

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“…While this may be a reasonable assumption for integrated cross sections, recent work has shown it is certainly wrong for differential cross sections (i.e., photoelectron angular distributions). Experiments have shown the importance of nondipole effects in the 1-3 keV photon-energy region [8,9], in the hundreds-of-eV range [10], and, in one case, at 13 eV [11]. Concurrently, theory has predicted significant nondipole contributions to electron angular distributions for atomic valence shells down to threshold at a few tens of eV photon energy [12 -14].…”

mentioning

confidence: 99%

Dramatic Nondipole Effects in Low-Energy Photoionization: Experimental and Theoretical Study of Xe5s

et al. 2003

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The Xe 5s nondipole photoelectron parameter is obtained experimentally and theoretically from threshold to 200 eV photon energy. Significant nondipole effects are seen even in the threshold region of this valence shell photoionization. In addition, contrary to previous understanding, clear evidence of interchannel coupling among quadrupole photoionization channels is found. DOI: 10.1103/PhysRevLett.91.053002 PACS numbers: 31.25.Eb, 32.80.Fb Until recently, conventional wisdom had assumed nondipole effects in photoionization were negligible at relatively low photon energies, perhaps for energies up to a few keV, but certainly for photon energies below a few hundred eV [1][2][3]. Indeed, despite indications to the contrary [4 -7], the usual practice in the field of photoionization, particularly for experiment, had been to ignore effects beyond the dipole approximation for photon energies as high as several keV. While this may be a reasonable assumption for integrated cross sections, recent work has shown it is certainly wrong for differential cross sections (i.e., photoelectron angular distributions). Experiments have shown the importance of nondipole effects in the 1-3 keV photon-energy region [8,9], in the hundreds-of-eV range [10], and, in one case, at 13 eV [11]. Concurrently, theory has predicted significant nondipole contributions to electron angular distributions for atomic valence shells down to threshold at a few tens of eV photon energy [12 -14].In addition, for dipole photoionization, interchannel coupling, which is simply configuration interaction in the continuum, has been shown to be important for most subshells of most atoms at most energies [15,16]; this work was contrary to the previous conventional wisdom that the independent-particle approximation (IPA) was generally valid away from thresholds. It had been suggested, however, that such interchannel coupling was not important in quadrupole photoionization channels [17], but recent theory has suggested that interchannel coupling can indeed be significant in quadrupole photoionization channels as well [14].To test these two ideas, significant nondipole contributions to the photoionization of a valence shell in the threshold region, and the existence of interchannel coupling effects in quadrupole photoionization channels, we have performed a benchmark experiment on the differential photoionization cross section of Xe 5s from 26 eV (close to threshold) to 200 eV to obtain the nondipole contribution to the photoelectron angular distribution which arises from interference between dipole (E1) and quadrupole (E2) channels. The differential cross section is given by [6,[18][19][20] where is the angle-integrated cross section, is the dipole anisotropy parameter, P 2 cos 3cos 2 ÿ 1=2, and and are nondipole asymmetry parameters. The coordinate axes have the positive x axis along the direction of the photon propagation vector, the z axis along the photon polarization vector, and and are the polar and azimuthal angles of the photoelectron momentum vector. ...

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Beyond the dipole approximation: angular-distribution effects in valence photoemission

Cited by 101 publications

References 24 publications

Non-dipole effects in the angular distribution of photoelectrons in sequential two-photon atomic double ionization

Non-dipole effects in the angular distribution of photoelectrons in sequential two-photon atomic double ionization

Atomic Auger Doppler effects upon emission of fast photoelectrons

Dramatic Nondipole Effects in Low-Energy Photoionization: Experimental and Theoretical Study of Xe5s

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