| 1. |
- Varju, Katalin, et al.
(författare)
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Experimental studies of attosecond pulse trains
- 2005
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Ingår i: Laser Physics. - 1054-660X. ; 15:6, s. 888-898
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental measurements of attosecond pulse trains. The characterization of the pulses uses a spectral interferometry technique that is implemented with a Mach-Zehnder interferometer. This allows us to manipulate independently the pump and probe pulses for a wide range of applications. By letting the attosecond pulses pass through metallic films, we can in particular compensate for the intrinsic chirp of the attosecond pulses corresponding to the plateau spectral region, thus getting pulses as short as 170 attoseconds-only 1.2 optical cycles at the central frequency. The measurement technique is also applicable for determination of the group delay of thin XUV-transparent films and relative delay in the photoionization process. Our experimental method is applied to attosecond pulse trains created by 35- and 9-fs laser pulses, and the shortest train observed consists of three or four pulses.
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| 2. |
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| 3. |
- Sola, I. J., et al.
(författare)
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Temporal and spectral studies of high-order harmonics generated by polarization-modulated infrared fields
- 2006
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 74:1
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Tidskriftsartikel (refereegranskat)abstract
- The temporal confinement of high harmonic generation (HHG) via modulation of the polarization of the fundamental pulse is studied in both temporal and spectral domains. In the temporal domain, a collinear cross-correlation setup using a 40 fs IR pump for the HHG and a 9 fs IR pulse to probe the generated emission is used to measure the XUV pulse duration. The observed temporal confinement is found to be consistent with theoretical predictions. An increased confinement is observed when a 9 fs pulse is used to generate the harmonics. An important spectral broadening, including a continuum background, is also measured. Theoretical calculations show that with 10 fs driving pulses, either one or two main attosecond pulses are created depending on the value of the carrier envelope phase.
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| 4. |
- Strelkov, V, et al.
(författare)
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Attosecond pulses generation with an ellipticity-modulated laser pulse
- 2005
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Ingår i: Laser Physics. - 1054-660X. ; 15:6, s. 871-879
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Tidskriftsartikel (refereegranskat)abstract
- Attosecond pulse emission using a laser field with time-dependent ellipticity is studied experimentally and theoretically. Our theoretical approach is validated by comparison with experimental VUV spectra. We show in calculations that the VUV emission can be confined into a narrow temporal window in which the fundamental polarization is quasi-linear. We find an analytical equation describing the duration of this window and compare it with numerical results. The requirements for the fundamental field that are necessary to confine this emission to a single attosecond pulse generation are formulated.
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| 5. |
- Strelkov, V, et al.
(författare)
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Generation of attosecond pulses with ellipticity-modulated fundamental
- 2004
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 78:7-8, s. 879-884
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Tidskriftsartikel (refereegranskat)abstract
- We have studied experimentally and theoretically high-order harmonic generation using a laser field with a time-dependent ellipticity. We show that the harmonic emission can be confined into a narrow temporal window, in which the fundamental polarization is quasi-linear. This allows a single attosecond pulse (200 as) with a fundamental field obtained from 10 fs pulse to be generated.
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| 6. |
- Strelkov, V, et al.
(författare)
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Single attosecond pulse production with an ellipticity-modulated driving IR pulse
- 2005
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - 0953-4075. ; 38:10, s. 161-167
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically study attosecond pulse production via high-harmonic generation using a driving laser pulse with a time-dependent ellipticity. The theoretical approach produces results that agree with our experimental data obtained using 35 fs driving laser pulses and is further used to study the generation of single attosecond pulses with shorter laser pulses. We find an equation for the duration of the temporal window created by the time-varying driving laser polarization in which high-harmonic emission can occur. We formulate the necessary requirements concerning the driving laser field in order to confine the high-harmonic emission in the form of a single attosecond pulse. Indeed, we show that using incident 12 fs laser pulses single attosecond pulses can be produced for certain carrier-envelope phase (CEP) values of the driving pulse. For 6 fs incident laser pulses, single attosecond pulses are produced for all values of the CEP (the intensity of the attosecond pulse still depends on the actual value of the CEP). If implemented with state-of-the-art 5 A laser pulses, this technique can even lead to the production of sub-100 as pulses.
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| 7. |
- Zaïr, A., et al.
(författare)
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Confinement of attosecond train pulses by using a modulated polarization IR pulse
- 2005
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Ingår i: 2005 Conference on Lasers and Electro-Optics Europe. - 0780389743 - 9780780389748
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Konferensbidrag (refereegranskat)abstract
- We study the temporal and spectral behaviour of high order harmonics generated by pulses with temporally modulated polarization. We observe a harmonic temporal confinement and a harmonic spectral broadening, compatible with 1 -or-2 attosecond pulse emission.
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| 8. |
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| 9. |
- Balcou, P, et al.
(författare)
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High-order-harmonic generation: towards laser-induced phase-matching control and relativistic effects
- 2002
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 74:6, s. 509-515
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Tidskriftsartikel (refereegranskat)abstract
- We present a review of some recent results on high-order-harmonic generation, aiming at optimizing the photon flux to allow for future applications in extreme-ultra-violet non-linear optics. We first present new schemes to control phase matching of high harmonics in gases, by using the effect of the spatially varying atomic phase displayed by the high harmonics. An enhancement by a factor of 50 is observed in neon in conditions for which the gradient of the atomic dispersion balances the electronic dispersion. A new scheme to manipulate the laser field was demonstrated, and shown to improve phase matching. We then turn to high-harmonic generation by solid targets, and show that high harmonics generated by an intense 30-fs laser pulse remain collimated even at the threshold of the relativistic regime.
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| 10. |
- 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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