| 1. |
- Altucci, C, et al.
(författare)
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Frequency-resolved time-gated high-order harmonics
- 1998
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 58:5, s. 3934-3941
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Tidskriftsartikel (refereegranskat)abstract
- We report measurements of high-order harmonic spectra obtained with a 800-nm 150-fs loser pulse with a time-varying degree of ellipticity. The modulation of the polarization in time is achieved by using birefringent optics and self-phase modulation in a glass plate. We can create one or two temporal gates of a few femtoseconds width, during which the polarization is linear and harmonic emission is efficient. The harmonic spectra observed experimentally demonstrate that harmonics generated with linear polarization are frequency chirped. The values measured experimentally are consistent with theoretical predictions based on the strong field approximation. [S1050-2947(98)05511-5].
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| 2. |
- 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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| 3. |
- Fill, E, et al.
(författare)
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Xuv Spectra of Optical-field-ionized Plasmas
- 1995
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Ingår i: Physical Review E: covering statistical, nonlinear, biological, and soft matter physics. - 1063-651X. ; 51:6, s. 6016-6027
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Tidskriftsartikel (refereegranskat)
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| 4. |
- 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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| 5. |
- Starczewski, Tomas
(författare)
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Generation of coherent short-wavelength radiation --- High-order harmonics and x-ray lasers
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The recent availability of short-pulse, high-intensity, compact lasers has opened doors to new and fascinating areas in atomic physics. Using the Lund Terawatt Laser, the interaction of femtosecond, near-infrared and visible laser radiation with matter at intensities in the range 1013--1017 W/cm2 was studied. Out of many phenomena that occur in this intensity range, this thesis deals with two: the short-wavelength amplification of the spontaneous emission in plasmas created from solid and gas targets, and the generation of high-order harmonics of the fundamental laser frequency. Both phenomena can serve as a basis for the generation of short-wavelength, coherent radiation, which is of great interest in many scientific and industrial applications.
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| 6. |
- Starczewski, Tomas, et al.
(författare)
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Time-resolved Harmonic-generation In An Ionizing Gas
- 1994
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 27:14, s. 3291-3301
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Tidskriftsartikel (refereegranskat)abstract
- We report on a time-resolved study of the fifth harmonic generated in xenon by 140 ps pulses from a Nd:YAG laser in the 10(13) W cm-2 intensity regime. Absolute timing between the driving laser pulse and the harmonic pulse could be determined by means of reference harmonics generated in non-linear crystals and a single common streak camera. Above a certain laser intensity the centre of the observed harmonic pulse was shifted earlier in time relative to the laser pulse. We found the intensity dependence of this shift to be approximately linear within the intensity range used which is consistent with the results of numerical simulations taking the ionization and dispersion of the xenon gas into account.
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