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| 2. |
- Erman, P, et al.
(författare)
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Autoionization Widths of the No Rydberg-valence State Complex In the 11-12 Ev Region
- 1995
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 239:1-3, s. 6-10
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Tidskriftsartikel (refereegranskat)abstract
- The photoion excitation spectra of (NO)-N-14 and (NO)-N-15 have been studied in the 105-112 Mn excitation region using high-order harmonic laser spectroscopy. Utilizing the small bandwidth offered by this technique, the natural widths of prominent lines in this region have been measured. These lines originate from interactions between high-lying Rydberg levels converging to the NO+ electronic ground state and a 'new' NO valence state situated close to the latter state. The present measurements show broad resonances corresponding to a decay time of 20-50 fs. This supports the interpretation that the decay takes place via rapid electronic autoionization.
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| 3. |
- Roos, L, et al.
(författare)
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Controlling phase matching of high-order harmonic generation by manipulating the fundamental field
- 1999
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 60:6, s. 5010-5018
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Tidskriftsartikel (refereegranskat)abstract
- We study experimentally how to control and improve phase matching of high-order harmonic generation. We use a birefringent lens and a birefringent compensator to obtain a fundamental laser pulse (150 fs, 800 nm, similar to 4 mJ) With two foci Separated by 6.2 mm along the propagation axis and with a controllable phase delay between the polarizations along the optic axes of the birefringent optical components. This enables us to enhance the high-order harmonic conversion efficiency for the high-order harmonics in neon to 3 x 10(-8), a factor of 4 higher compared to a single-focus setup in similar conditions. The enhancement is achieved by improving the phase matching and at the same time maintaining a high intensity in a large generating volume. [S1050-2947(99)04512-6].
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| 4. |
- Altucci, C, et al.
(författare)
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Influence of atomic density in high-order harmonic generation
- 1996
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Ingår i: Optical Society of America. Journal B: Optical Physics. - 0740-3224. ; 13:1, s. 148-156
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated how high-order harmonics generated in rare gases depend on the atomic density. The peak and the profile of the atomic density in the interaction region were measured as a function of the backing pressure and the distance from the nozzle by a differential interferometry technique, The conversion efficiency for the harmonics in the plateau was found to increase approximately quadratically over the entire range of peak pressures investigated (3-80 mbar). The intensity of the harmonics in the cutoff region, in contrast, increased only until an optimum peak pressure was reached, beyond which it decreased. This optimum peak pressure was found to be dependent on both the laser intensity and the process order. To understand this effect, we have performed extensive propagation calculations of both the fundamental and the harmonic fields, using ionization rates and dipole moments from a tunnel ionization model. We obtained good agreement with the experimental results. The observed effect is attributed to ionization-induced defocusing of the fundamental laser beam, which reduces the peak intensity obtained in the medium and shortens the extent of the plateau. (C) 1996 Optical Society of America
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| 5. |
- Gaarde, Mette, et al.
(författare)
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Spatiotemporal separation of high harmonic radiation into two quantum path components
- 1999
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 59:2, s. 1367-1373
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Tidskriftsartikel (refereegranskat)abstract
- We present a spatiotemporal analysis of high harmonic generation, showing evidence for the presence of several quantum path contributions to the atomic dipole moment. We show that the harmonic radiation can largely be described as a sum of two fields having a phase proportional to the intensity of the generating field. We compare our results to recent experimental results demonstrating this separation [M. Bellini et al., Phys. Rev. Lett. 81, 297 (1998)]. We show how the temporal and spatial coherence properties are influenced by this effect, and discuss how it could be used to obtain better control of the generated harmonic radiation. [S1050-2947(99)00402-3].
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| 6. |
- Larsson, Jörgen, et al.
(författare)
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Two-color Time-resolved Spectroscopy of Helium Using High-order Harmonics
- 1995
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 28:3
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Tidskriftsartikel (refereegranskat)abstract
- The radiative lifetime of the 1s2p(1)P state of helium is measured in a two-colour ionization experiment with a 5% accuracy. The state is excited by the 13th harmonic of a tunable 80 ps laser and ionized by a synchronous ultraviolet laser, with a variable time delay. This experiment demonstrates that the high harmonics generated in a jet of rare gas exposed to an intense laser field provide a tunable short-pulse xuv source ideally suited for pump/probe type of studies and, in particular, short lifetime measurements.
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| 7. |
- Larsson, J., et al.
(författare)
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Two-colour time-resolved spectroscopy of helium using high-order harmonics
- 1995
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 28:3, s. 53-58
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Tidskriftsartikel (refereegranskat)abstract
- The radiative lifetime of the ls2p1P state of helium is measured in a two-colour ionization experiment with a 5% accuracy. The state is excited by the 13th harmonic of a tunable SO ps laser and ionized by a synchronous ultraviolet laser, with a variable time delay. This experiment demonstrates that the high harmonics generated in a jet of rare gas exposed to an intense laser field provide a tunable short-pulse xuv source ideally suited for pump/probe type of studies and, in particular, short lifetime measurements.
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| 8. |
- L'Huillier, Anne, et al.
(författare)
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High-order Harmonics - A Coherent Source In the Xuv Range
- 1995
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Ingår i: Journal of Nonlinear Optical Physics & Materials. - 0218-1991. ; 4:3, s. 647-665
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Tidskriftsartikel (refereegranskat)abstract
- We review the main results concerning high-order generation processes from the point of view of a potential user of this new source of XUV radiation. The perspectives for optimizing the source, both in efficiency and in spectral range, its characteristics and in particular, its coherence properties, are discussed. Finally, we describe two experiments, which demonstrate the usefulness of the harmonics as a short-pulse, coherent source in the XUV domain.
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| 9. |
- Mercer, I, et al.
(författare)
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Spatial mode control of high-order harmonics
- 1996
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Ingår i: Physical Review Letters. - 1079-7114. ; 77:9, s. 1731-1734
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the spatial mode of high-order harmonics can be continuously controlled. The control is achieved by spatially modulating the degree of elliptical polarization of the fundamental field using birefringent optics. A highly sensitive relationship between the efficiency of harmonic generation and the degree of laser elliptical polarization leads to atoms emitting harmonics mainly in regions of linear polarization. The harmonics are emitted as annular beams whose angles of divergence can be continuously varied.
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