Field-induced ionization and Coulomb explosion of nitrogen |
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Authors: | CY Wu HZ Ren TT Liu R Ma H Yang HB Jiang QH Gong |
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Institution: | (1) State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, P.R. China, CN |
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Abstract: | Femtosecond-laser field-induced ionization and Coulomb explosion of diatomic nitrogen were systematically investigated using
time-of-flight mass and photoelectron spectrometry. Both linearly and circularly polarized femtosecond laser pulses were used
at intensities varying from 5×1013 to 2×1015 W/cm2. Strong N2
+, N2
2+, N+, N2+ and N3+ ion signals were observed for horizontally polarized pulses. Moreover, signals from the atomic ions exhibited a double-peak
structure. Suppression of ionization was observed for circularly polarized pulses, while for vertically polarized pulses,
only N2
+ and N2
2+ ions were observed. The angular distributions of the ions were measured under zero-field conditions in the ionization zone.
The atomic ions N+, N2+ and N3+ exhibited highly anisotropic distributions, with maxima along the laser polarization vector and zeroes normal to the laser
polarization vector. In contrast to the atomic ions, N2
+ exhibited a strong isotropic angular distribution. These observations indicate that dynamic alignment is responsible for
the observed anisotropic angular distribution of the atomic ions. The kinetic energy spectrum of the photoelectrons is featureless
and broad, extending above the ponderomotive potential of the laser pulse. The angular distribution is markedly anisotropic,
with a maximum along the laser polarization vector. These observations further support the notion that the field-ionization
mechanism is dominant under our experimental conditions.
Received: 29 January 2002 / Revised version: 15 March 2002 / Published online: 12 July 2002 |
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Keywords: | PACS: 42 50 Hz 33 15 Ta 33 60 -q |
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