| 1. |
- Hickstein, Daniel D., et al.
(författare)
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Direct Visualization of Laser-Driven Electron Multiple Scattering and Tunneling Distance in Strong-Field Ionization
- 2012
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Ingår i: Physical Review Letters. - 1079-7114. ; 109:7
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Tidskriftsartikel (refereegranskat)abstract
- Using a simple model of strong-field ionization of atoms that generalizes the well-known 3-step model from 1D to 3D, we show that the experimental photoelectron angular distributions resulting from laser ionization of xenon and argon display prominent structures that correspond to electrons that pass by their parent ion more than once before strongly scattering. The shape of these structures can be associated with the specific number of times the electron is driven past its parent ion in the laser field before scattering. Furthermore, a careful analysis of the cutoff energy of the structures allows us to experimentally measure the distance between the electron and ion at the moment of tunnel ionization. This work provides new physical insight into how atoms ionize in strong laser fields and has implications for further efforts to extract atomic and molecular dynamics from strong-field physics.
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| 2. |
- Ranitovic, Predrag, et al.
(författare)
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IR-assisted ionization of helium by attosecond extreme ultraviolet radiation
- 2010
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 12, s. 13008-
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Tidskriftsartikel (refereegranskat)abstract
- Attosecond science has opened up the possibility of manipulating electrons on their fundamental timescales. Here, we use both theory and experiment to investigate ionization dynamics in helium on the attosecond timescale by simultaneously irradiating the atom with a soft x-ray attosecond pulse train (APT) and an ultrafast laser pulse. Because the APT has resolution in both energy and time, we observe processes that could not be observed without resolution in both domains simultaneously. We show that resonant absorption is important in the excitation of helium and that small changes in energies of harmonics that comprise the APT can result in large changes in the ionization process. With the help of theory, ionization pathways for the infrared-assisted excitation and ionization of helium by extreme ultraviolet (XUV) attosecond pulses have been identified and simple model interpretations have been developed that should be of general applicability to more complex systems (Zewail A 2000 J. Phys. Chem. A 104 5660-94).
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| 3. |
- Ranitovic, Predrag, 1974-
(författare)
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Time-Resolved Attosecond Spectroscopy of He Using COLTRIMS
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tunable ultrafast lasers are becoming a standard tool for probing and controlling the dynamics of atoms, molecules and chemical reactions. This thesis is a contribution to a large, ongoing effort to make spectroscopic tools for inducing and controlling, in real time, the natural processes which occur on the femto and attosecond times scales.Femtosecond lasers, with a fundamental wavelength in the infrared (IR) spectral region, can be used for producing a fascinating spectroscopic tool - extreme ultraviolet (XUV) pulses with typical duration of hundreds of attoseconds. A typical XUV attosecond pulse is produced when an intense ultrafast laser is focused in a gaseous target. The fundamental laser frequency gets upconverted into its higher harmonics through an extreme nonlinear process in which the electron leaves the ion's potential well and oscillates in the laser field emitting a short burst of radiation every time it is driven back into the vicinity of its parent ion by the linearly polarized laser electric field. In this thesis, we present several examples of using IR and XUV pulses to induce and control the excitation and ionization processes in atoms and molecules on the attosecond time scale. A 3D momentum imaging technique called COLTRIMS is used to collect all the reaction products (electrons and ions) in coincidence.The experiments were performed at the J.R.M. lab at the Kansas State University, where the experimental apparatus was designed and built under the supervision of professor C.L. Cocke.
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| 4. |
- Singh, K. P., et al.
(författare)
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Control of Electron Localization in Deuterium Molecular Ions using an Attosecond Pulse Train and a Many-Cycle Infrared Pulse
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:2, s. 23001-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an experimental control of electron localization in deuterium molecular ions created and dissociated by the combined action of an attosecond pulse train and a many-cycle infrared (IR) pulse. The attosecond pulse train is synthesized using both even and odd high order harmonics of the driving IR frequency so that it can strobe the IR field once per IR cycle. An asymmetric ejection of the deuterium ions oscillates with the full IR period when the APT-IR time-delay is scanned. The observed control is due to the creation of a coherent superposition of 1s sigma(g) and 2p sigma(u) states via interference between one-photon and two-photon dissociation channels.
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