| 1. |
- Johnsson, Per, et al.
(författare)
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Attosecond control of ionization by wave-packet interference
- 2007
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Ingår i: Physical Review Letters. - 1079-7114. ; 99:23
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Tidskriftsartikel (refereegranskat)abstract
- A train of attosecond pulses, synchronized to an infrared (IR) laser field, is used to create a series of electron wave packets (EWPs) that are below the ionization threshold in .helium. The ionization probability is found to strongly oscillate with the delay between the IR and attosecond fields twice per IR laser cycle. Calculations that reproduce the experimental results demonstrate that this ionization control results from interference between transiently bound EWPs created by different pulses in the train. In this way, we are able to observe, for the first time, attosecond wave-packet interference in a strongly driven atomic system.
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| 2. |
- Johnsson, Per, et al.
(författare)
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Attosecond electron wave packet dynamics in strong laser fields
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 95:1, s. 1-013001
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Tidskriftsartikel (refereegranskat)abstract
- We use a train of sub-200 attosecond extreme ultraviolet (XUV) pulses with energies just above the ionization threshold in argon to create a train of temporally localized electron wave packets. We study the energy transfer from a strong infrared (IR) laser field to the ionized electrons as a function of the delay between the XUV and IR fields. When the wave packets are born at the zero crossings of the IR field, a significant amount of energy (similar to 20 eV) is transferred from the field to the electrons. This results in dramatically enhanced above-threshold ionization in conditions where the IR field alone does not induce any significant ionization. Because both the energy and duration of the wave packets can be varied independently of the IR laser, they are valuable tools for studying and controlling strong-field processes.
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| 3. |
- 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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| 4. |
- Kelkensberg, F., et al.
(författare)
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Molecular Dissociative Ionization and Wave-Packet Dynamics Studied Using Two-Color XUV and IR Pump-Probe Spectroscopy
- 2009
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Ingår i: Physical Review Letters. - 1079-7114. ; 103:12
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined theoretical and experimental study of ultrafast wave-packet dynamics in the dissociative ionization of H-2 molecules as a result of irradiation with an extreme-ultraviolet (XUV) pulse followed by an infrared (IR) pulse. In experiments where the duration of both the XUV and IR pulses are shorter than the vibrational period of H-2+, dephasing and rephasing of the vibrational wave packet that is formed in H-2+ upon ionization of the neutral molecule by the XUV pulse is observed. In experiments where the duration of the IR pulse exceeds the vibrational period of H-2+ (15 fs), a pronounced dependence of the H+ kinetic energy distribution on XUV-IR delay is observed that can be explained in terms of the adiabatic propagation of the H-2+ wave packet on field-dressed potential energy curves.
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| 5. |
- Lepine, F., et al.
(författare)
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Short XUV pulses to characterize field-free molecular alignment
- 2007
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Ingår i: Journal of Modern Optics. - : Informa UK Limited. - 0950-0340 .- 1362-3044. ; 54:7, s. 953-966
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Tidskriftsartikel (refereegranskat)abstract
- We present experiments on field-free molecular alignment of N-2 and CO2 probed with short XUV pulses that are obtained via high-harmonic generation. The XUV pulses induce a dissociative ionization or a Coulomb explosion of the molecule, where the fragment ion recoil (measured using the velocity map imaging technique) provides information on the alignment of the parent molecule at the time of ionization. We discuss how photoelectron detection may in future allow the determination of molecular-frame photoelectron angular distributions and molecular structure.
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| 6. |
- 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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| 7. |
- Mauritsson, Johan, et al.
(författare)
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Attosecond Electron Spectroscopy Using a Novel Interferometric Pump-Probe Technique
- 2010
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Ingår i: Physical Review Letters. - 1079-7114. ; 105:5
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Tidskriftsartikel (refereegranskat)abstract
- We present an interferometric pump-probe technique for the characterization of attosecond electron wave packets (WPs) that uses a free WP as a reference to measure a bound WP. We demonstrate our method by exciting helium atoms using an attosecond pulse (AP) with a bandwidth centered near the ionization threshold, thus creating both a bound and a free WP simultaneously. After a variable delay, the bound WP is ionized by a few-cycle infrared laser precisely synchronized to the original AP. By measuring the delay-dependent photoelectron spectrum we obtain an interferogram that contains both quantum beats as well as multipath interference. Analysis of the interferogram allows us to determine the bound WP components with a spectral resolution much better than the inverse of the AP duration.
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| 8. |
- 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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| 9. |
- Remetter, Thomas
(författare)
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Attosecond Electron Wave Packet Interferences
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Attosecond pulses offer a new route to produce temporally localized electron wave packets (EWPs) that can easily be tailored by altering the properties of the attosecond pulses. In this thesis we will present different experiments, supported by theory, where attosecond EWPs are created in presence of a strong infrared (IR) field. By tuning the central frequency of the attosecond pulses and/or changing the target gas, the initial energy of the wave packets is set to be either above, or below the ionization potential. In a first set of experiments, trains of free attosecond EWPs separated by half a laser period are created by single photon ionization. Depending on the timing of ionization compared to the external IR field, a shear and/or a phase difference between the consecutive EWPs is induced. Because the EWPs are created coherently, interferences depending on their phase difference will occur. The analysis of the interferograms enables to retrieve information about the phase of the EWPs. In a second set of experiments, bound electron wave packets are created below the ionization potential of a target gas. In the case of a train of bound EWPs, we find that the ionization is greatly enhanced by the presence of the infrared laser field and that this enhancement strongly depends on the timing between the attosecond pulses and the laser field. We show that this effect can be attributed to interference between consecutive wave packets. In the case of a single bound EWP, we are able to probe its time evolution with a short IR pulse.
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| 10. |
- Remetter, Thomas, et al.
(författare)
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Attosecond electron wave packet interferometry
- 2006
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 2:5, s. 323-326
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Tidskriftsartikel (refereegranskat)abstract
- A complete quantum-mechanical description of matter and its interaction with the environment requires detailed knowledge of a number of complex parameters. In particular, information about the phase of wavefunctions is important for predicting the behaviour of atoms, molecules or larger systems. In optics, information about the evolution of the phase of light in time(1) and space(2) is obtained by interferometry. To obtain similar information for atoms and molecules, it is vital to develop analogous techniques. Here we present an interferometric method for determining the phase variation of electronic wave packets in momentum space, and demonstrate its applicability to the fundamental process of single-photon ionization. We use a sequence of extreme-ultraviolet attosecond pulses(3,4) to ionize argon atoms and an infrared laser field, which induces a momentum shear(5) between consecutive electron wave packets. The interferograms that result from the interaction of these wave packets provide useful information about their phase. This technique opens a promising new avenue for reconstructing the wavefunctions(6,7) of atoms and molecules and for following the ultrafast dynamics of electronic wave packets.
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