| 1. |
- Arnold, Cord L., et al.
(författare)
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Spatiotemporal coupling of attosecond pulses
- 2019
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Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. - 9781728104690 ; Part F140-CLEO_Europe 2019
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Konferensbidrag (refereegranskat)abstract
- Attosecond pulses in the extreme ultraviolet (XUV) spectral range are today routinely generated via high-order harmonic generation (HHG), when intense ultrashort laser pulses are focused into a gaseous generation medium. The effect is most easily understood in a semi-classical picture [1]. An electron can tunnel ionize from the distorted atomic potential, pick up kinetic energy in the laser field, potentially return to its parent ion and recombine. The excess energy is emitted as XUV photon. The process repeats for every half-cycle of the driving field, resulting in a train of attosecond pulses and in the frequency domain in the well-known, odd-order comb of harmonics. Two main families of electron trajectories leading to the same photon energy can be distinguished into 'short' and 'long', according to their time of travel in the continuum. Due to the complicated nature of the HHG process, attosecond pulses usually cannot be separated into their temporal and spatial profiles, but instead have strong chromatic aberration and are spatio-temporally coupled [2-4].
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| 2. |
- Campi, Filippo, et al.
(författare)
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Design and test of a broadband split-and-delay unit for attosecond XUV-XUV pump-probe experiments.
- 2016
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 87:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the design of a split-and-delay unit for the production of two delayed replicas of an incident extreme ultraviolet (XUV) pulse. The device features a single grazing incidence reflection in combination with attenuation of remaining infrared light co-propagating with the XUV beam, offering a high throughput without the need of introducing additional optics that would further decrease the XUV flux. To achieve the required spatial and temporal stabilities, the device is controlled by two PID-controllers monitoring the delay and the beam pointing using an optical reference laser beam, making collimation of the beam by additional optics unnecessary. Finally, we demonstrate the stability of the split-and-delay unit by performing all-reflective autocorrelation measurements on broadband few-cycle laser pulses.
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| 3. |
- Coudert-Alteirac, Hélène, et al.
(författare)
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Micro-focusing of broadband high-order harmonic radiation by a double toroidal mirror
- 2017
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 7:11
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Tidskriftsartikel (refereegranskat)abstract
- We present an optical system based on two toroidal mirrors in aWolter configuration to focus broadband extreme ultraviolet (XUV) radiation. Optimization of the focusing optics alignment is carried out with the aid of an XUV wavefront sensor. Back-propagation of the optimized wavefront to the focus yields a focal spot of 3.6 × 4.0 μm2 full width at half maximum, which is consistent with ray-tracing simulations that predict a minimum size of 3.0 × 3.2 μm2. This work is important for optimizing the intensity of focused high-order harmonics in order to reach the nonlinear interaction regime.
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| 4. |
- Coudert-Alteirac, Helene
(författare)
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Spatial and temporal metrology of intense attosecond pulses
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Attosecond pulses are short enough to capture the electronic dynamics in atoms and molecules. The work presented in this thesis deals with the generation and optimization of attosecond extreme-ultraviolet (XUV) pulses. The goal is to progress towards the realization of time-resolved nonlinear experiments at the intense XUV beamline of the Lund High-Power Laser Facility.The XUV flux was optimized using a loose focusing geometry. This led to a formalization of scaling laws for high-order harmonic generation (HHG) and more generally for nonlinear optics in gases, e.g., filamentation. A high intensity on target was achieved by focusing the high XUV flux using a pair of toroidal mirrors in a Wolter-like configuration.Spatial properties of the high-order harmonics were studied in details. Wavefront measurements of the harmonics were performed, both in the far field and after the refocusing optics, as well as spectrally resolved measurements. The origin of XUV aberrations is discussed, and the variation of the harmonic divergence depending on the generation position relative to the fundamental focus is studied.The intense XUV beamline and its first nonlinear experiments are presented. An interferometer to split-and-delay the beam was developed. Tests were performed, showing the capacity to provide attosecond resolution fortime-resolved experiments in the beamline.The high XUV intensity on target combined with the attosecond interferometer opens the door to perform XUV-pump XUV-probe experiments.
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| 5. |
- Dacasa, Hugo, et al.
(författare)
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Single-shot extreme-ultraviolet wavefront measurements of high-order harmonics
- 2019
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Ingår i: Optics Express. - 1094-4087. ; 27:3, s. 2656-2670
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Tidskriftsartikel (refereegranskat)abstract
- We perform wavefront measurements of high-order harmonics using an extreme-ultraviolet (XUV) Hartmann sensor and study how their spatial properties vary with different generation parameters, such as pressure in the nonlinear medium, fundamental pulse energy and duration as well as beam size. In some conditions, excellent wavefront quality (up to 휆/11) was obtained. The high throughput of the intense XUV beamline at the Lund Laser Centre allows us to perform single-shot measurements of both the full harmonic beam generated in argon and individual harmonics selected by multilayer mirrors. We theoretically analyze the relationship between the spatial properties of the fundamental and those of the generated high-order harmonics, thus gaining insight into the fundamental mechanisms involved in high-order harmonic generation (HHG).
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| 6. |
- Gyan, D. S., et al.
(författare)
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Low-temperature nanoscale heat transport in a gadolinium iron garnet heterostructure probed by ultrafast x-ray diffraction
- 2022
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Ingår i: Structural Dynamics-Us. - : AIP Publishing. - 2329-7778. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved x-ray diffraction has been used to measure the low-temperature thermal transport properties of a Pt/Gd3Fe5O12//Gd3Ga5O12 metal/oxide heterostructure relevant to applications in spin caloritronics. A pulsed femtosecond optical signal produces a rapid temperature rise in the Pt layer, followed by heat transport into the Gd3Fe5O12 (GdIG) thin film and the Gd3Ga5O12 (GGG) substrate. The time dependence of x-ray diffraction from the GdIG layer was tracked using an accelerator-based femtosecond x-ray source. The ultrafast diffraction measurements probed the intensity of the GdIG (1 -1 2) x-ray reflection in a grazing-incidence x-ray diffraction geometry. The comparison of the variation of the diffracted x-ray intensity with a model including heat transport and the temperature dependence of the GdIG lattice parameter allows the thermal conductance of the Pt/GdIG and GdIG//GGG interfaces to be determined. Complementary synchrotron x-ray diffraction studies of the low-temperature thermal expansion properties of the GdIG layer provide a precise calibration of the temperature dependence of the GdIG lattice parameter. The interfacial thermal conductance of the Pt/GdIG and GdIG//GGG interfaces determined from the time-resolved diffraction study is of the same order of magnitude as previous reports for metal/oxide and epitaxial dielectric interfaces. The thermal parameters of the Pt/GdIG//GGG heterostructure will aid in the design and implementation of thermal transport devices and nanostructures. (C) 2022 Author(s).
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| 7. |
- Heyl, C. M., et al.
(författare)
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Scale-invariant nonlinear optical effects in gases
- 2016
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Ingår i: 2016 Conference on Lasers and Electro-Optics, CLEO 2016. - 9781943580118
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Konferensbidrag (refereegranskat)abstract
- A general scaling formalism for nonlinear light-matter interactions in gases is presented and experimentally verified. The formalism enables to conveniently extrapolate nonlinear phenomena, such as filamentation or high-order harmonic generation, to new laser parameters.
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| 8. |
- Heyl, C. M., et al.
(författare)
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Scaling Nonlinear Optics in Gases
- 2016
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Ingår i: High Intensity Lasers and High Field Phenomena, HILAS 2016. - 9781943580095 ; Part F15-HILAS 2016
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Konferensbidrag (refereegranskat)abstract
- Extrapolating nonlinear phenomena, such as filamentation, to new parameters as e.g. to higher pulse energy is often challenging. We here present a general scaling model for nonlinear light-matter interactions in gases and proof it experimentally.
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| 9. |
- Jensen, Maja, 1978, et al.
(författare)
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High-resolution macromolecular crystallography at the FemtoMAX beamline with time-over-threshold photon detection
- 2021
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Ingår i: Journal of Synchrotron Radiation. - 1600-5775 .- 0909-0495. ; 28, s. 64-70
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Tidskriftsartikel (refereegranskat)abstract
- Protein dynamics contribute to protein function on different time scales. Ultrafast X-ray diffraction snapshots can visualize the location and amplitude of atom displacements after perturbation. Since amplitudes of ultrafast motions are small, high-quality X-ray diffraction data is necessary for detection. Diffraction from bovine trypsin crystals using single femtosecond X-ray pulses was recorded at FemtoMAX, which is a versatile beamline of the MAX IV synchrotron. The time-over-threshold detection made it possible that single photons are distinguishable even under short-pulse low-repetition-rate conditions. The diffraction data quality from FemtoMAX beamline enables atomic resolution investigation of protein structures. This evaluation is based on the shape of the Wilson plot, cumulative intensity distribution compared with theoretical distribution, I/σ, Rmerge /Rmeas and CC1/2 statistics versus resolution. The FemtoMAX beamline provides an interesting alternative to X-ray free-electron lasers when studying reversible processes in protein crystals.
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| 10. |
- Maclot, Sylvain, et al.
(författare)
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Dissociation dynamics of the diamondoid adamantane upon photoionization by XUV femtosecond pulses
- 2020
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Ingår i: Scientific Reports. - : Nature Research. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a photodissociation study of the diamondoid adamantane using extreme ultraviolet femtosecond pulses. The fragmentation dynamics of the dication is unraveled by the use of advanced ion and electron spectroscopy giving access to the dissociation channels as well as their energetics. To get insight into the fragmentation dynamics, we use a theoretical approach combining potential energy surface determination, statistical fragmentation methods and molecular dynamics simulations. We demonstrate that the dissociation dynamics of adamantane dications takes place in a two-step process: barrierless cage opening followed by Coulomb repulsion-driven fragmentation.
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| 11. |
- Maclot, Sylvain, et al.
(författare)
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Towards XUV-pump XUV-probe experiments with attosecond pulses at the Lund Laser Centre
- 2015
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635, s. 112079-112079
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Konferensbidrag (refereegranskat)abstract
- The relaxation dynamics of an ionized/excited molecular system leads to different fundamental processes occurring at sub-femtosecond timescales. Time-resolved XUV-pump XUV-probe experiments should allow deeper insight to the key roles of these processes. Such studies should be feasible soon thanks to experimental schemes similar to those at the high-intensity high-order harmonic generation beamline at the Lund Laser Centre.
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| 12. |
- Rading, Linnea, et al.
(författare)
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A versatile velocity map ion-electron covariance imaging spectrometer for high-intensity XUV experiments
- 2018
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 8:6
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Tidskriftsartikel (refereegranskat)abstract
- We report on the design and performance of a velocity map imaging (VMI) spectrometer optimized for experiments using high-intensity extreme ultraviolet (XUV) sources such as laser-driven high-order harmonic generation (HHG) sources and free-electron lasers (FELs). Typically exhibiting low repetition rates and high single-shot count rates, such experiments do not easily lend themselves to coincident detection of photo-electrons and -ions. In order to obtain molecular frame or reaction channel-specific information, one has to rely on other correlation techniques, such as covariant detection schemes. Our device allows for combining different photo-electron and -ion detection modes for covariance analysis. We present the expected performance in the different detection modes and present the first results using an intense high-order harmonic generation (HHG) source.
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| 13. |
- Wikmark, Hampus, et al.
(författare)
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Spatiotemporal coupling of attosecond pulses
- 2019
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424. ; 116:11, s. 4779-4787
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Tidskriftsartikel (refereegranskat)abstract
- The shortest light pulses produced to date are of the order of a few tens of attoseconds, with central frequencies in the extreme UV range and bandwidths exceeding tens of electronvolts. They are often produced as a train of pulses separated by half the driving laser period, leading in the frequency domain to a spectrum of high, odd-order harmonics. As light pulses become shorter and more spectrally wide, the widely used approximation consisting of writing the optical waveform as a product of temporal and spatial amplitudes does not apply anymore. Here, we investigate the interplay of temporal and spatial properties of attosecond pulses. We show that the divergence and focus position of the generated harmonics often strongly depend on their frequency, leading to strong chromatic aberrations of the broadband attosecond pulses. Our argument uses a simple analytical model based on Gaussian optics, numerical propagation calculations, and experimental harmonic divergence measurements. This effect needs to be considered for future applications requiring highquality focusing while retaining the broadband/ultrashort characteristics of the radiation.
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