| 1. |
- Dahlström, Marcus, et al.
(författare)
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Atomic and macroscopic measurements of attosecond pulse trains
- 2009
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 80:3
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Tidskriftsartikel (refereegranskat)abstract
- We characterize attosecond pulses in a train using both the well established "reconstruction of attosecond beating by interference of two-photon transitions" (RABITT) technique and the recently demonstrated in situ method, which is based on a weak perturbation of the harmonic generation process by the second harmonic of the laser field. The latter technique determines the characteristics of the single atom emission, while RABITT allows one to measure attosecond pulses "on target." By comparing the results of the two methods, the influence of propagation and filtering on the attosecond pulses can be extracted.
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| 2. |
- Johnsson, Per, et al.
(författare)
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Trains of attosecond electron wave packets
- 2006
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Ingår i: Journal of Modern Optics. - : Informa UK Limited. - 0950-0340 .- 1362-3044. ; 53:1-2, s. 233-245
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Tidskriftsartikel (refereegranskat)abstract
- We study temporally localized electron wave packets, generated using a train of extreme ultraviolet (XUV) attosecond pulses to ionize the target atoms. Both the electron wave packets and the attosecond pulse train ( APT) are characterized using the same technique, based on interference of two-photon transitions in the continuum. We study, in particular, the energy transfer from a moderately strong infrared (IR) field to the electron wave packets as a function of time delay between the XUV and the IR fields. The use of an APT to generate the electron wave packets enables the generation at times not accessible through tunneling ionization. We find that a significant amount of energy is transferred from the IR field to the electron wave packets, when they are generated at a zero-crossing of the IR laser field. This energy transfer results in a dramatically enhanced above-threshold ionization even at IR intensities that alone are not strong enough to induce any significant ionization.
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| 3. |
- Mansten, Erik, et al.
(författare)
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Broadband attosecond pulse shaping
- 2007
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Ingår i: Optics Letters. - 0146-9592. ; 32:11, s. 1353-1355
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Tidskriftsartikel (refereegranskat)abstract
- We use semiconductor (Si) and metallic (Al, Zr) transmission filters to shape, in amplitude and phase, high-order harmonics generated from the interaction of an intense titanium sapphire laser field with a pulsed neon gas target. Depending on the properties of the filter, the emitted attosecond pulses can be optimized in bandwidth and/or pulse length. We demonstrate the generation of attosecond pulses centered at energies from 50 to 80 eV, with bandwidths as large as 45 eV and with pulse durations compressed to 130 as. (c) 2007 Optical Society of America.
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| 4. |
- Mansten, Erik
(författare)
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Measurement and Control of Attosecond Light Fields
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Attosecond pulses are used to study electron dynamics in atoms and molecules. In this thesis, schemes to control the generation of attosecond pulses and pulse-shaping techniques to compress the pulses are presented. Generation of attosecond pulses requires high intensity, which is reached by focusing a pulsed femtosecond laser. The emitted pulses come isolated or in an attosecond pulse train (APT), depending on the duration of the driving field. In several experiments, we have controlled the pulse repetition rate in the APT by adding the second harmonic to the driving field. An APT with one pulse per cycle of the driving field is then generated, instead of a train with two pulses per cycle, which is the case for a one-color field. A rather strong second harmonic changes the shape of the generating field, which leads to a tunable central photon energy of the attosecond pulses. With a short driving field an APT containing few pulses is generated. The spectrum of a short APT shows additional interference structures. In analogy with multi-slit interference, these structures are secondary maxima, positioned in between the principal maxima. The number of secondary maxima is related to the number of pulses in the APT. Attosecond pulses are emitted by a macroscopic medium. How the macroscopic conditions affect the pulse duration has also been studied. Directly after the generation the attosecond pulses have, in general, a relatively long pulse duration. Spectral filtering is important to shape the spectrum and compress the pulses. We have used thin transmission filters and multi-layer XUV-mirrors for filtering. We measured a pulse duration of 130 as, for attosecond pulses generated in Ne and filtered by Zr. Most schemes to characterize attosecond pulses are based on a cross-correlation with an IR field. We have used the RABITT (reconstruction of attosecond beating by interference of two-photon transitions) and the AC-streak camera techniques, capable of measuring different types of APT:s. Finally, attosecond pulses have been used in two application experiments: Momentum shearing interferometry; and the Quantum stroboscope, where electron scattering off the atomic potential was observed.
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| 5. |
- Mansten, Erik, et al.
(författare)
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Spectral shaping of attosecond pulses using two-colour laser fields
- 2008
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- We use a strong two-colour laser field composed of the fundamental (800 nm) and the second harmonic (400 nm) of an infrared (IR) laser field to generate attosecond pulses with controlled spectral and temporal properties. With a second-harmonic intensity equal to 15% of the IR intensity the second-harmonic field is strong enough to significantly alter and control the electron trajectories in the generation process. This enables us to tune the central photon energy of the attosecond pulses by changing the phase difference between the IR and the second-harmonic fields. In the time domain the radiation is emitted as a sequence of pulses separated by a full IR cycle. We also perform calculations showing that the effect of even stronger second-harmonic fields leads to an extended tunable range under conditions that are experimentally feasible.
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| 6. |
- Mansten, Erik, et al.
(författare)
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Spectral signature of short attosecond pulse trains.
- 2009
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Ingår i: Physical Review Letters. - 1079-7114. ; 102:8
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Tidskriftsartikel (refereegranskat)abstract
- We report experimental measurements of high-order harmonic spectra generated in Ar using a carrier-envelope-offset (CEO) stabilized 12 fs, 800 nm laser field and a fraction (less than 10%) of its second harmonic. Additional spectral peaks are observed between the harmonic peaks, which are due to interferences between multiple pulses in the train. The position of these peaks varies with the CEO and their number is directly related to the number of pulses in the train. An analytical model, as well as numerical simulations, support our interpretation.
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| 7. |
- Mauritsson, Johan, et al.
(författare)
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Attosecond pulse trains generated using two color laser fields
- 2006
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Ingår i: Physical Review Letters. - 1079-7114. ; 97:1
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the spectral and temporal structure of high harmonic emission from argon exposed to an infrared laser field and its second harmonic. For a wide range of generating conditions, trains of attosecond pulses with only one pulse per infrared cycle are generated. The synchronization necessary for producing such trains ensures that they have a stable pulse-to-pulse carrier envelope phase, unlike trains generated from one color fields, which have two pulses per cycle and a pi phase shift between consecutive pulses. Our experiment extends the generation of phase stabilized few cycle pulses to the extreme ultraviolet regime.
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| 8. |
- Mauritsson, Johan, et al.
(författare)
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Coherent electron scattering captured by an attosecond quantum stroboscope.
- 2008
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Ingår i: Physical Review Letters. - 1079-7114. ; 100:7
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a quantum stroboscope based on a sequence of identical attosecond pulses that are used to release electrons into a strong infrared (IR) laser field exactly once per laser cycle. The resulting electron momentum distributions are recorded as a function of time delay between the IR laser and the attosecond pulse train using a velocity map imaging spectrometer. Because our train of attosecond pulses creates a train of identical electron wave packets, a single ionization event can be studied stroboscopically. This technique has enabled us to image the coherent electron scattering that takes place when the IR field is sufficiently strong to reverse the initial direction of the electron motion causing it to rescatter from its parent ion.
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| 9. |
- Mauritsson, Johan, et al.
(författare)
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Sub-cycle control of attosecond pulse generation using two-colour laser fields
- 2009
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Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 42:13
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Konferensbidrag (refereegranskat)abstract
- Strong field laser-matter interaction is intrinsically a sub-cycle phenomenon, which is clearly illustrated by the generation of attosecond pulses through the high-order harmonic process. Therefore, to control strong field processes the structure of the field driving the generation has to be controlled on a sub-cycle level. One approach is to use phase stabilized few-cycle driving pulses and vary the carrier-envelope phase of these pulses; an alternative method is to use longer pulses and include the second harmonic to tailor the field structure.
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| 10. |
- Morlens, AS, et al.
(författare)
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Design and characterization of extreme-ultraviolet broadband mirrors for attosecond science
- 2006
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Ingår i: Optics Letters. - 0146-9592. ; 31:10, s. 1558-1560
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Tidskriftsartikel (refereegranskat)abstract
- A novel multilayer mirror was designed and fabricated based on a recently developed three-material technology aimed both at reaching reflectivities of about 20% and at controlling dispersion over a bandwidth covering photon energies between 35 and 50 eV. The spectral phase upon reflection was retrieved by measuring interferences in a two-color ionization process using high-order harmonics produced from a titanium: sapphire laser. We demonstrate the feasibility of designing and characterizing phase-controlled broadband optics in the extreme-ultraviolet domain, which should facilitate the manipulation of attosecond pulses for applications.
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