Precision measurements of the absolute photoionization cross sections of He

Samson, James A. R.; He, Z. X.; Yin, Liang; Haddad, G. N.

doi:10.1088/0953-4075/27/5/008

Cited by 175 publications

(236 citation statements)

References 34 publications

(16 reference statements)

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“…The values represent a compilation of the experimental data given in Refs. [18][19][20][21][22][23][24][25][26][27][28] keV. To further increase the detector sensitivity, the X-GMD has the option to collect photoions created over the comparably large distance of 20 cm along the photon beam by means of an additional extraction field maintained by an aperture system ͑see Fig.…”

Section: Gmds For Hard X-ray Felsmentioning

confidence: 99%

Gas detectors for x-ray lasers

Tiedtke¹,

Feldhaus²,

Hahn³

et al. 2008

Journal of Applied Physics

161

128

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We have developed different types of photodetectors that are based on the photoionization of a gas at a low target density. The almost transparent devices were optimized and tested for online photon diagnostics at current and future x-ray free-electron laser facilities on a shot-to-shot basis with a temporal resolution of better than 100 ns. Characterization and calibration measurements were performed in the laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II in Berlin. As a result, measurement uncertainties of better than 10% for the photon-pulse energy and below 20 m for the photon-beam position were achieved at the Free-electron LASer in Hamburg ͑FLASH͒. An upgrade for the detection of hard x-rays was tested at the Sub-Picosecond Photon Source in Stanford.

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Section: Gmds For Hard X-ray Felsmentioning

confidence: 99%

Gas detectors for x-ray lasers

Tiedtke¹,

Feldhaus²,

Hahn³

et al. 2008

Journal of Applied Physics

161

128

View full text Add to dashboard Cite

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“…In this limit, Eqs. (3,4) implies an electron spectrum in coincidence with He ++ (displayed schematically in Fig. 1) with two Rydberg series symmetrically centered around the energy…”

Section: Scenario For Two-photon Double Ionization By Attosecond mentioning

confidence: 99%

“…Recently, the two-photon double-ionization and above-threshold ionization of helium were experimentally observed with the Ti:sapphire 27th harmonic pulses (photon energy 41.8 eV) [3]. These experimental advances open up the opportunity to revisit the dynamics of double ionization of helium by XUV photons previously investigated only in the singlephoton absorption and scattering regime using synchrotron radiation [4,5]. Simultaneous ejection of two electrons by a single photon allowed detailed tests of wavefunctions for the three-body Coulomb problem [6,7,8] and the role of electron correlations in strongly inelastic processes accompanied with near-zero momentum transfer (photoabsorption) or sizable momentum transfer (Compton scattering) [9,10].…”

Section: Introductionmentioning

confidence: 99%

Angular distribution in two-photon double ionization of helium by intense attosecond soft-x-ray pulses

2006

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We investigate two-photon double ionization of helium by intense (≈ 10 15 W/cm 2 ) ultrashort (≈ 300 as) soft X-ray pulses (E = 91.6 eV). The time-dependent two-electron Schrödinger equation is solved using a coupled channel method. We show that for ultrashort pulses the angular distribution of ejected electrons depends on the pulse duration and provides novel insights into the role of electron correlations in the two-electron photoemission process. The angular distribution at energies near the "independent electron" peaks is close to dipolar while it acquires in the "valley" of correlated emission a significant quadrupolar component within a few hundred attoseconds.

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“…We use the revised approach of Pavlov (1994a) (Kirby et al, 1979). The revised photoionization and photoabsorption cross sections are taken from Richards et al (1994a); these authors did not publish the photoionization cross section for He, and for these we have used values from Samson et al (1994). The revised electron cooling rates by vibrational and rotational excitation of O 2 and N 2 given by Pavlov (1998a, b) are included in the updated IZMIRAN model.…”

Section: Theoretical Modelmentioning

confidence: 99%

The role of vibrationally excited oxygen and nitrogen in the ionosphere during the undisturbed and geomagnetic storm period of 6-12 April 1990

Павлов

1998

Ann. Geophys.

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Abstract. We present a comparison of the observed behavior of the F-region ionosphere over Millstone Hill during the geomagnetically quiet and storm periods of 6±12 April 1990 with numerical model calculations from the IZMIRAN time-dependent mathematical model of the Earth's ionosphere and plasmasphere. The major enhancement to the IZMIRAN model developed in this study is the use of a new loss rate of O 4 S ions as a result of new high-temperature¯owing afterglow measurements of the rate coe cients u 1 and u 2 for the reactions of O 4 S with N 2 and O 2 . The deviations from the Boltzmann distribution for the ®rst ®ve vibrational levels of O 2 v were calculated, and the present study suggests that these deviations are not signi®cant. It was found that the di erence between the non-Boltzmann and Boltzmann distribution assumptions of O 2 v and the di erence between ion and neutral temperature can lead to an increase of up to about 3% or a decrease of up to about 4% of the calculated NmF2 as a result of a respective increase or a decrease in u 2 . The IZMIRAN model reproduces major features of the data. We found that the inclusion of vibrationally excited N 2 v b 0 and O 2 v b 0 in the calculations improves the agreement between the calculated NmF2 and the data on 6, 9, and 10 April. However, both the daytime and nighttime densities are reproduced by the IZMIRAN model without the vibrationally excited nitrogen and oxygen on 8 and 11 April better than the IZMIRAN model with N 2 v b 0 and O 2 v b 0 . This could be due to possible uncertainties in model neutral temperature and densities, EUV¯uxes, rate coe cients, and the¯ow of ionization between the ionosphere and plasmasphere, and possible horizontal divergence of the¯ux of ionization above the station. Our calculations show that the increase in the O N 2 rate factor due to N 2 v b 0 produces a 5± 36% decrease in the calculated daytime peak density. The increase in the O O 2 loss rate due to vibrationally excited O 2 produces 8±46% reductions in NmF2. The e ects of vibrationally excited O 2 and N 2 on x e and e are most pronounced during the daytime.

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Precision measurements of the absolute photoionization cross sections of He

Cited by 175 publications

References 34 publications

Gas detectors for x-ray lasers

Gas detectors for x-ray lasers

Angular distribution in two-photon double ionization of helium by intense attosecond soft-x-ray pulses

The role of vibrationally excited oxygen and nitrogen in the ionosphere during the undisturbed and geomagnetic storm period of 6-12 April 1990

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