| 1. |
- Cacciani, P., et al.
(author)
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Lifetime measurements of the e1II, v = 0 and v = 1 states of12C16O, 13C16O, and13C18O
- 1998
-
In: Astrophysical Journal. - 0004-637X. ; 499:2 PART II, s. 223-226
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Journal article (peer-reviewed)abstract
- In a laboratory investigation using tunable picosecond lasers in a pump-probe configuration, lifetimes of the E 1u, v = 0 and v = 1 states of CO are experimentally determined. For E 'D, v = 1, the lifetime is found to vary significantly for the isotopomers. Combining the data with existing oscillator strengths, predissociation probabilities within the range of 93.6%-98.6% result for 12C16O, 13C16O, and 13C18O in the case of the E 1u, v = I state, which is the state that predominantly influences the isotopic fractionation of CO in interstellar clouds.
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| 2. |
- Cacciani, P, et al.
(author)
-
Lifetime measurements of the E (1)Pi, upsilon=0 and upsilon=1 states of (CO)-C-12-O-16, (CO)-C-13-O-16, and (CO)-C-13-O-18
- 1998
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X. ; 499
-
Journal article (peer-reviewed)abstract
- In a laboratory investigation using tunable picosecond lasers in a pump-probe configuration, lifetimes of the E (II)-I-1, v = O and v = 1 states of CO are experimentally determined. For E (II)-I-1, v = 1, the lifetime is found to vary significantly for the isotopomers. Combining the data with existing oscillator strengths, predissociation probabilities within the range of 93.6%-98.64% result for (CO)-C-12-O-16, (CO)-C-13-O-16, and (CO)-C-13-O-18 in, the case of the E (II)-I-1, v=1 state, which is the state that predominantly influences the isotopic fractionation of CO in interstellar clouds.
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| 3. |
- Lynga, C, et al.
(author)
-
Temporal coherence of high-order harmonics
- 1999
-
In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 60:6, s. 4823-4830
-
Journal article (peer-reviewed)abstract
- Systematic studies of the temporal coherence properties of high-order harmonic radiation are presented. These complement our previous investigations [Bellini et at, Phys. Rev. Lett. 81, 297 (1998)], where we showed the separation of the far-field pattern of high-order harmonics into two distinct spatial regions with different coherence times. Here we show how the coherence time of the inner and outer regions changes as a function of the harmonic order, the laser intensity, and the focusing conditions. Good agreement with the predictions of the semiclassical model of harmonic generation is obtained. [S1050-2947(99)10312-3].
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| 4. |
- Sikstrom, C. M, et al.
(author)
-
New Zr II oscillator strengths and the zirconium conflict in the HgMn star chi Lupi
- 1999
-
In: Astronomy & Astrophysics. - 0004-6361. ; 343:1, s. 297-302
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Journal article (peer-reviewed)abstract
- Lifetimes on the sub-nanosecond scale for the levels v(2)D(3/2), v(2)F(3/2) and v(2)F(5/2) in the 4d5s5p configuration in Zr II have been measured, using the method of laser-induced fluorescence. Combined with branching fractions obtained with the Lund Ultraviolet (UV) Fourier Transform Spectrometer (FTS), experimental oscillator strengths have been derived. From Hubble Space Telescope/Goddard High-Resolution Spectrograph spectra, the zirconium abundance in the HgMn star chi Lupi has been determined from Zr II and Zr III lines. More than an order of magnitude difference in the Zr II abundance has been derived from these ionization stages. The difference is much too large to be explained by uncertainties in the oscillator strengths. Possible explanations of this difference have to be found in the stellar models, such as the influence of non-LTE or diffusion.
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| 5. |
- Zerne, R, et al.
(author)
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Phase-locked high-order harmonic sources
- 1997
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In: Physical Review Letters. - 1079-7114. ; 79:6, s. 1006-1009
-
Journal article (peer-reviewed)abstract
- We demonstrate that two harmonic sources generated independently in a xenon gas jet using the same picosecond Nd:YAG laser are locked in phase. The experiment is performed by separating a laser beam into two parallel beams focused at different locations under the nozzle of a gas jet, and therefore producing two independent sources of harmonic radiation, and studying the pattern obtained in the far field when the radiations from these sources interfere. A high and robust fringe visibility is obtained.
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| 6. |
- Bellini, M, et al.
(author)
-
Temporal coherence of ultrashort high-order harmonic pulses
- 1998
-
In: Physical Review Letters. - 1079-7114. ; 81:2, s. 297-300
-
Journal article (peer-reviewed)abstract
- We have studied the temporal coherence of high-order harmonics (up to the 15th order) produced by focusing 100 fs laser pulses into an argon gas jet. We measure the visibility of the interference fringes, produced when two spatially separated harmonic sources interfere in the far field, as a function of the time delay between the two sources. In general, we find long coherence times, comparable to the expected pulse durations of the harmonics. For some of the harmonics, the interference pattern exhibits two regions, with significantly different coherence times. These results are interpreted in terms of different electronic trajectories contributing to harmonic generation. [S0031-9007(98)05569-7].
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| 7. |
- Biemont, E, et al.
(author)
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Radiative lifetimes, branching fractions and transition probabilities in Ge I - solar implications
- 1999
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In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 303:4, s. 721-726
-
Journal article (peer-reviewed)abstract
- New radiative lifetimes have been measured for the 5s (3)P(0,1,2)degrees and 5s (1)P(1)degrees levels of Ge I using a laser-produced plasma subject to selective laser excitation. A diffraction grating based emission spectrometer of moderately high resolution has been used to remeasure the branching ratios of the 4p-5s depopulating transitions. The oscillator strengths of astrophysical interest, which have been derived from these new data, are compared with theoretical values calculated within a pseudo-relativistic Hartree-Fock approach. The new set of f-values has been compared with the few results available in the literature, which are generally characterized by a large scatter and a low accuracy. The solar photospheric abundance of germanium deduced from the new atomic data of the present work is A(Ge) = 3.58 +/- 0.05, on the usual logarithmic scale, in agreement with the meteoritic value.
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| 8. |
- Lynga, C, et al.
(author)
-
High-order harmonic generation in molecular gases
- 1996
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In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 29:14, s. 3293-3302
-
Journal article (peer-reviewed)abstract
- We present an experimental study of harmonic generation in molecular gases, using the fundamental (800 nm) and the second harmonic (400 nm) of a 150 fs titanium - sapphire laser at an intensity of ##IMG## [http://ej.iop.org/images/0953-4075/29/14/032/img1.gif] . We compare the conversion efficiency and the maximum energy obtained in different species: rare gases (Ar, Xe), diatomic molecules ( ##IMG## [http://ej.iop.org/images/0953-4075/29/14/032/img2.gif] , ##IMG## [http://ej.iop.org/images/0953-4075/29/14/032/img3.gif] , ##IMG## [http://ej.iop.org/images/0953-4075/29/14/032/img4.gif] , CO) and polyatomic molecules ( ##IMG## [http://ej.iop.org/images/0953-4075/29/14/032/img5.gif] , ##IMG## [http://ej.iop.org/images/0953-4075/29/14/032/img2.gif] O, ##IMG## [http://ej.iop.org/images/0953-4075/29/14/032/img7.gif] , ##IMG## [http://ej.iop.org/images/0953-4075/29/14/032/img8.gif] , ##IMG## [http://ej.iop.org/images/0953-4075/29/14/032/img9.gif] ). The harmonic spectra from molecular gases are very similar to those obtained in the atomic gases, with a plateau and a cutoff whose location is strongly correlated to the value of the ionization potential. The conversion efficiency is not higher than that of the rare gases.
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