| 1. |
- Erny, Christian, et al.
(författare)
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Metrology of high-order harmonics for free-electron laser seeding
- 2011
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- We examine the characteristics of high-order harmonics generated with 800 nm, 25 mJ, 160 fs laser pulses in an Ar gas cell with the objective of seeding a free electron laser. We measure the energy per pulse and per harmonic, the energy jitter, the divergence and the position stability of the harmonic beam. We perform ab initio numerical simulations based on integration of the time-dependent Schrodinger equation and of the wave equation within the slowly varying envelope approximation. The results reproduce the experimental measurements to better than a factor of two. The interaction of a frequency comb of harmonic fields with an electron bunch in an undulator is examined with a simple model consisting of calculating the energy modulation owing to the seed-electron interaction. The model indicates that the undulator acts as a spectral filter selecting a given harmonic.
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| 2. |
- Gabrysch, Markus, et al.
(författare)
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XUV-induced transient phase gratings for probing ultra-fast carrier generation and recombination processes in wide-bandgap semiconductors
- 2013
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Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 525:1-2, s. 59-65
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Tidskriftsartikel (refereegranskat)abstract
- A method for probing the temporal evolution of ultra-fast carrier generation and recombination processes in wide-bandgap semiconductors, e.g. diamond, is described. Two extreme ultraviolet (pump) pulses produced by high-order harmonic generation in Argon gas (with a photon energy of 32 eV) are superimposed on a sample with a small angle between them, inducing periodic changes in the refractive index of the material causing it to act as a transient diffraction grating. A delayed synchronized infrared (probe) pulse gets diffracted on the induced phase grating and is detected in the first diffraction order. By varying the time-delay between pump and probe, the full temporal evolution of the free carrier generation and recombination processes can be resolved. Feasibility calculations and the first steps towards experimental implementation are presented.
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| 3. |
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| 4. |
- He, Xinkui, et al.
(författare)
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Interference effects in two-color high-order harmonic generation
- 2010
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 82:3
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Tidskriftsartikel (refereegranskat)abstract
- We study high-order harmonic generation in argon driven by an intense 800 nm laser field and a small fraction of its second harmonic. The intensity and divergence of the emitted even and odd harmonics are strongly modulated as a function of the relative delay between the two fields. We provide a detailed analysis of the underlying interference effects. The interference changes drastically when approaching the cutoff region due to a switch of the dominant trajectory responsible for harmonic generation.
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| 5. |
- He, Xinkui, et al.
(författare)
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Spatial and spectral properties of the high-order harmonic emission in argon for seeding applications
- 2009
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 79:6
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Tidskriftsartikel (refereegranskat)abstract
- We characterize and control the harmonic emission in the spectral and spatial domains in order to define in which conditions the harmonic radiation can be a high-quality seed for soft x-ray and x-ray free-electron lasers. The length of the gas cell, where harmonics are generated, was optimized and the energy per pulse was determined in absolute value with a calibrated x-ray photodiode. The beam spatial profile was measured and, in some conditions, a very collimated beam with a half-angle divergence below 1 mrad could be obtained. We also show that increasing the intensity of the fundamental laser field leads to a considerable broadening of the bandwidth of the harmonic radiation, allowing us to cover a large spectral range. This effect is due to fundamental reshaping leading to an efficient phase matching of both short- and long-trajectory contributions.
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| 6. |
- Schwenke, Jörg, et al.
(författare)
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Digital in-line holography on amplitude and phase objects prepared with electron beam lithography.
- 2012
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720. ; 247:2, s. 196-201
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication and characterization of amplitude and phase samples consisting of well defined Au or Al features formed on ultrathin silicon nitride membranes. The samples were manufactured using electron beam lithography, metallization and a lift-off technique, which allow precise lateral control and thickness of the metal features. The fabricated specimens were evaluated by conventional microscopy, atomic force microscopy and with the digital in-line holography set-up at the Lund Laser Centre. The latter uses high-order harmonic generation as a light source, and is capable of recovering both the shape and phase shifting properties of the samples. We report on the details of the sample production and on the imaging tests with the holography set-up.
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| 7. |
- Schwenke, Jörg, et al.
(författare)
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Digital in-line holography with a single high-order harmonic pulse
- 2009
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Ingår i: Holography : Advances and Modern Trends - Advances and Modern Trends. - : SPIE. - 9780819476326 ; 7358
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Konferensbidrag (refereegranskat)abstract
- In this paper, we review the optimization and characterization of a high-order harmonic generation (HHG) source for application in coherence imaging, and the use of this light source in a digital in-line holography setup. The high-order harmonic beam is generated by focusing a powerful infrared beam into an Ar gas cell. The length of the cell and the focusing parameters are optimized to maximize the HHG output. By spectrally filtering and focusing the generated harmonic beam and positioning a 2D detector, we obtain a table-top light source suitable for in-line holography, capable of recording a hologram with a single 40 fs XUV pulse. The reconstructed images have a spatial resolution in the micrometer range.
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| 8. |
- Schwenke, Jörg, et al.
(författare)
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Single-shot holography using high-order harmonics
- 2008
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Ingår i: Journal of Modern Optics. - : Informa UK Limited. - 0950-0340 .- 1362-3044. ; 55:16, s. 2723-2730
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Tidskriftsartikel (refereegranskat)abstract
- This work demonstrates single-shot holography with ultrashort XUV pulses. The pulses are generated by high-harmonic generation in an Ar gas cell and focused to produce a strongly divergent reference beam suitable for in-line holography of micrometer size objects. The achieved intensity of the high-order harmonics in the XUV regime is sufficient for single-shot holography with good signal-to-noise ratio. A numerical algorithm is applied to reconstruct real images from the recorded holograms, which also includes an iterative process to reduce the twin-image blurring. Holograms and reconstructed images of microscope tips are presented and a description of the algorithm is given.
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