| 11. |
- Gaarde, Mette, et al.
(författare)
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High-order tunable sum and difference frequency mixing in the xuv region
- 1996
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 29:5
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of tunable high-order sum and difference frequency mixing in the 7-70 eV range, in xenon, argon and neon. We mix the light from a terawatt, subpicosecond titanium-sapphire laser and that from a tunable optical parametric generator. The radiation generated through mixing processes involves absorption or emission of one or Mo photons from the weak tunable source. The relative strengths of the sum and difference frequency processes depend strongly on the wavelength range of the generated radiation. The sum frequency processes are stronger at low photon energies in xenon, whereas the difference frequency processes dominate at high photon energies, in neon, being almost comparable to harmonic generation.
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| 12. |
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| 13. |
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| 14. |
- Gratz, M, et al.
(författare)
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Time-gated imaging in radiology: Theoretical and experimental studies
- 1996
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Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 1077-260X. ; 2:4, s. 1041-1048
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Tidskriftsartikel (refereegranskat)abstract
- Novel short-pulse X-ray sources, e.g., laser-produced plasmas, offer new approaches to the solution of the scatter-reduction problem in X-ray imaging, by the use of time-gated detection techniques. Monte Carlo simulations are used to estimate the scatter-reduction performance of time-gated imaging techniques within a range of X-ray energies, gating times and tissue parameters, Significant improvements can be achieved for thick tissues combined with high photon energies, Experimental studies on water phantoms are performed using a laser-produced plasma X-ray source. Problems arising on the technical realization are discussed.
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| 15. |
- Herrlin, K, et al.
(författare)
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Contrast-enhanced radiography by differential absorption, using a laser-produced X-ray source
- 1997
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Ingår i: Investigative Radiology. - 0020-9996. ; 32:5, s. 306-310
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Tidskriftsartikel (refereegranskat)abstract
- RATIONALE AND OBJECTIVES. The authors evaluate the feasibility of differential imaging of contrast media, with division of individual pixel values obtained from digital images generated by characteristic radiation from a laser-produced plasma, bridging the K-absorption edge of the contrast agent. METHODS. Laser pulses from an ultrashort-pulse terawatt laser system were focused onto gadolinium and tantalum targets, creating a plasma from which characteristic radiation and Bremsstrahlung was emitted. The elements of the target were selected so the characteristic emission lines of one of the elements were below the K edge of the contrast agent and the emission lines of the other element above. A phantom with gadolinium and other elements in various concentrations was examined. One radiographic exposure was made using a gadolinium target source and a subsequent exposure using a tantalum source. Both images were recorded digitally and the transmission ratios calculated by division of the individual pixel values. RESULTS. When viewed separately, the two images of the test phantom appeared similar. In the differential image, only the gadolinium solutions were bright, reflecting a difference in attenuation between the two exposures. CONCLUSIONS. Element-specific radiographs can be obtained by differential imaging. When fully explored, the technique may allow for contrast-enhanced radiography with increased sensitivity and decreased contrast dose.
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| 16. |
- Hunsche, S, et al.
(författare)
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Ionization and fragmentation of C-60 via multiphoton-multiplasmon excitation
- 1996
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Ingår i: Physical Review Letters. - 1079-7114. ; 77:10, s. 1966-1969
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Tidskriftsartikel (refereegranskat)abstract
- We study the intensity dependence of ionization and fragmentation of buckminsterfullerene (C-60) in strong laser fields. Our data provide strong evidence that at intensities less than or similar to 10(14) W/cm(2) these processes occur predominantly via multiphoton excitation of the 20 eV plasmon resonance of C-60 At least two plasmons have to be created to initiate fragmentation or multiple ionization.
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| 17. |
- Kohlweyer, S, et al.
(författare)
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Harmonic generation from solid-vacuum interface irradiated at high laser intensities
- 1995
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Ingår i: Optics Communications. - 0030-4018. ; 117:5-6, s. 431-438
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Tidskriftsartikel (refereegranskat)abstract
- Observations of harmonic generation from solid Al targets irradiated at intensities of 1017 W/cm2 using a tabletop Ti:sapphire terawatt laser system are reported. For irradiances with laser light at a wavelength of [lambda] = 794nm (the fundamental frequency), harmonics up to the 7th, while for irradiances with frequency doubled laser light ([lambda] = 397) nm harmonics up to the 4th of the respective incident radiation were detected.
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| 18. |
- 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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| 19. |
- 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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| 20. |
- Li, Z. S, et al.
(författare)
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Radiative properties of neutral germanium obtained from excited-state lifetime and branching-ratio measurements and comparison with theoretical calculations
- 1999
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 60:1, s. 198-208
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Tidskriftsartikel (refereegranskat)abstract
- Using time-resolved UV laser-induced fluorescence from a laser-produced plasma, natural radiative lifetimes have been measured for 21 levels of Ge I belonging to the odd-parity 4p4d, 4p5d, and 4p6s configurations. Stimulated Brillouin scattering in water has allowed us to compress Nd:YAG laser pulses pumping a dye laser (where YAG denotes yttrium aluminum garnet), thus yielding 1-ns tunable laser pulses to enable accurate measurements of short lifetimes. Branching ratios of Ge I have been measured by inductively coupled plasma emission spectrometry, the intensity calibration being performed by means of Ar lines emitted by a hollow-cathode lamp. The experimental lifetimes and branching ratios have been combined in order to provide a set of accurate transition probabilities for the 4p-5s and 4p-4d transitions. A relativistic Hartree-Fock; calculation, taking configuration-interaction and polarization effects into account, has been combined with a least-squares optimization procedure of the Slater and spin-orbit integrals in order to test the ability of this approach to correctly predict radiative properties of the group-IV elements. Good agreement between experimental and theoretical transition probability values has been achieved for most of the transitions considered.
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