| 1. |
- Cheng, Y. C., et al.
(författare)
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Can we break the symmetry along the polarization axis in photoionization?
- 2020. - 7
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Ingår i: Attosecond Physics. - : IOP Publishing. - 1742-6588. ; 1412
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Konferensbidrag (refereegranskat)abstract
- Photoionization is a fundamental process in which an electron is emitted from an atom. The emission is traditionally considered to be symmetric with respect to the polarization axis, unless it is temporally confined to a period shorter than an optical cycle time. We demonstrate that this symmetry can still be broken by combining a train of a few attosecond pulses and a dressing laser field. The light fields act as temporal slits and phase modulator that releases electron wavepackets. The resulting photoelectron spectra differ for electrons emitted in opposite direction along the polarization.
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| 2. |
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| 3. |
- Zhong, Jin Hui, et al.
(författare)
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Nonlinear plasmon-exciton coupling enhances sum-frequency generation from a hybrid metal/semiconductor nanostructure
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The integration of metallic plasmonic nanoantennas with quantum emitters can dramatically enhance coherent harmonic generation, often resulting from the coupling of fundamental plasmonic fields to higher-energy, electronic or excitonic transitions of quantum emitters. The ultrafast optical dynamics of such hybrid plasmon–emitter systems have rarely been explored. Here, we study those dynamics by interferometrically probing nonlinear optical emission from individual porous gold nanosponges infiltrated with zinc oxide (ZnO) emitters. Few-femtosecond time-resolved photoelectron emission microscopy reveals multiple long-lived localized plasmonic hot spot modes, at the surface of the randomly disordered nanosponges, that are resonant in a broad spectral range. The locally enhanced plasmonic near-field couples to the ZnO excitons, enhancing sum-frequency generation from individual hot spots and boosting resonant excitonic emission. The quantum pathways of the coupling are uncovered from a two-dimensional spectrum correlating fundamental plasmonic excitations to nonlinearly driven excitonic emissions. Our results offer new opportunities for enhancing and coherently controlling optical nonlinearities by exploiting nonlinear plasmon-quantum emitter coupling.
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| 4. |
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| 5. |
- Arnbjornsson, E., et al.
(författare)
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The value of physiotherapy for faecal continence after correction of high anal atresia. A clinical and electromyographic study
- 1988
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Ingår i: Acta Chirurgica Scandinavica. - 0001-5482. ; 154:7-8, s. 467-470
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Tidskriftsartikel (refereegranskat)abstract
- A follow-up study of 12 patients who had undergone Stephens rectoplasty for high imperforate anus is presented. Clinical assessment and anal electromyography were performed more than 7 years after surgery, both before and after a year's physiotherapeutic training of the perianal musculature. Electromyography showed correlation between faecal continence and tonus of the anal sphincter, the anocutaneous reflex and maximal voluntary activity in the perianal muscles. After the physiotherapeutic training there was significant improvement of faecal continence. This effect was electromyographically corroborated. The results confirmed clinical observations that postoperative physiotherapy and training of the voluntary muscles in the perianal region is of value for the achievement of faecal continence.
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| 6. |
- Arnbjörnsson, E., et al.
(författare)
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Computed Tomography and Magnetic Resonance Tomography Findings in Children Operated for Anal Atresia
- 1990
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Ingår i: European Journal of Pediatric Surgery. - : Georg Thieme Verlag KG. - 0939-7248 .- 1439-359X. ; 45:3, s. 178-181
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Tidskriftsartikel (refereegranskat)abstract
- Computerised tomography and magnetic resonance tomography were performed in nine faecally incontinent patients more than eight years after rectoplasty for high imperforate anus. No statistically significant correlation was found between function, i. e. degree of faecal incontinence, and anatomical findings. Thus, in spite of a detailed demonstration of the post-operative anatomy, the information does not seem to be directly applicable in indicating a way to reoperate for faecal incontinence in this group of patients.
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| 7. |
- Arnold, Cord L., et al.
(författare)
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A high-repetition rate attosecond pulse source for coincidence spectroscopy
- 2021
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Ingår i: 2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021. - 9781665418768
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Konferensbidrag (refereegranskat)abstract
- The power of attosecond pump-probe spectroscopy combined with advanced detection schemes, such as photoelectron/ion coincidence spectrometers and time-resolved photoelectron emission microscopy (PEEM), can be unleashed by properly accounting for the repetition rate of the source. In this work, we present a high-repetition rate (200 kHz) attosecond pulse source that opens up for exploring phenomena, previously inaccessible to the community using attosecond interferometric and spectroscopy pump-probe techniques [1].
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| 8. |
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| 9. |
- Cheng, Yu Chen, et al.
(författare)
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Controlling photoionization using attosecond time-slit interferences
- 2020
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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. ; 117:20, s. 10727-10732
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Tidskriftsartikel (refereegranskat)abstract
- When small quantum systems, atoms or molecules, absorb a high-energy photon, electrons are emitted with a well-defined energy and a highly symmetric angular distribution, ruled by energy quantization and parity conservation. These rules are based on approximations and symmetries which may break down when atoms are exposed to ultrashort and intense optical pulses. This raises the question of their universality for the simplest case of the photoelectric effect. Here we investigate photoionization of helium by a sequence of attosecond pulses in the presence of a weak infrared laser field. We continuously control the energy of the photoelectrons and introduce an asymmetry in their emission direction, at variance with the idealized rules mentioned above. This control, made possible by the extreme temporal confinement of the light-matter interaction, opens a road in attosecond science, namely, the manipulation of ultrafast processes with a tailored sequence of attosecond pulses.
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| 10. |
- Guo, Chen, et al.
(författare)
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Phase control of attosecond pulses in a train
- 2018
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 51:3
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast processes in matter can be captured and even controlled by using sequences of few-cycle optical pulses, which need to be well characterized, both in amplitude and phase. The same degree of control has not yet been achieved for few-cycle extreme ultraviolet pulses generated by high-order harmonic generation (HHG) in gases, with duration in the attosecond range. Here, we show that by varying the spectral phase and carrier-envelope phase (CEP) of a high-repetition rate laser, using dispersion in glass, we achieve a high degree of control of the relative phase and CEP between consecutive attosecond pulses. The experimental results are supported by a detailed theoretical analysis based upon the semi-classical three-step model for HHG.
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| 11. |
- Harth, Anne, et al.
(författare)
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Compact 200 kHz HHG source driven by a few-cycle OPCPA
- 2018
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Ingår i: Journal of Optics (United Kingdom). - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 20:1
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Tidskriftsartikel (refereegranskat)abstract
- We present efficient high-order harmonic generation (HHG) based on a high-repetition rate, few-cycle, near infrared (NIR), carrier-envelope phase stable, optical parametric chirped pulse amplifier (OPCPA), emitting 6 fs pulses with 9 μJ pulse energy. In krypton, we reach conversion efficiencies from the NIR to the extreme ultraviolet (XUV) radiation pulse energy on the order of ∼10-6 with less than 3 μJ driving pulse energy. This is achieved by optimizing the OPCPA for a spatially and temporally clean pulse and by a specially designed high-pressure gas target. In the future, the high efficiency of the HHG source will be beneficial for high-repetition rate two-colour (NIR-XUV) pump-probe experiments, where the available pulse energy from the laser has to be distributed economically between pump and probe pulses.
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| 12. |
- Hoff, D., et al.
(författare)
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Direct CEP Stabilization of a high-repetition rate, few-cycle OPCPA chain with a single feedback loop, employing a Stereo-ATI
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - 9798350345995
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Konferensbidrag (refereegranskat)abstract
- Today's Carrier-Envelope Phase (CEP) stabilizations of mode-locked oscillators widely used in attosecond science and frequency metrology rely on octave spanning frequency combs and the detection of beating between the blue end and the frequency doubled red end of the same spectrum. This technique was established by the seminal works of Hänsch and co-workers [1], demonstrating the stabilization of optical frequencies from such a frequency comb by transferring the slippage of the CEP (or carrier-envelope offset frequency) into a detectable radio frequency by f-2f interferometry. The requirement of an octave spanning spectrum means that usually some kind of super-continuum generation is involved, which, in practice often is a fragile scheme since wide band oscillators are very prone to instabilities and noise.
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| 13. |
- Hoff, D., et al.
(författare)
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Quantum Beat Spectroscopy of Helium Photoelectrons
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - 9798350345995
-
Konferensbidrag (refereegranskat)abstract
- The availability of broadband extreme ultraviolet light sources allows for investigation of electron wave-packets from high lying bound states in atoms [1,2]. The dynamics of these states can be mapped out in the ionization continuum with an overlapping infrared field, which may also uncover new, light induced, dressed states [3]. Here, we carry out a complete characterization of these electron wave-packets using a small number of attosecond pulses.
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| 14. |
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| 15. |
- Isinger, M., et al.
(författare)
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Accuracy and precision of the RABBIT technique
- 2019
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Ingår i: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Science. - : The Royal Society. - 1364-503X .- 1471-2962. ; 377:2145
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Tidskriftsartikel (refereegranskat)abstract
- One of the most ubiquitous techniques within attosecond science is the so-called reconstruction of attosecond beating by interference of two-photon transitions (RABBIT). Originally proposed for the characterization of attosecond pulses, it has been successfully applied to the accurate determination of time delays in photoemission. Here, we examine in detail, using numerical simulations, the effect of the spatial and temporal properties of the light fields and of the experimental procedure on the accuracy of the method. This allows us to identify the necessary conditions to achieve the best temporal precision in RABBIT measurements. This article is part of the theme issue 'Measurement of ultrafast electronic and structural dynamics with X-rays'.
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| 16. |
- Jusko, Christoph, et al.
(författare)
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Spatio-temporal characterization of a femtosecond filament along its length
- 2020
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Ingår i: High Intensity Lasers and High Field Phenomena, HILAS 2020. - 9781557528209
-
Konferensbidrag (refereegranskat)abstract
- We present an experimental method capable of characterizing spatio-temporal dynamics of a femtosecond filament v ia F ourier t ransform i nterferometry, p roviding a three-dimensional reconstruction of the driving pulse, while scanning along the entire length of the filament.
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| 17. |
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| 18. |
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| 19. |
- Langer, Fabian, et al.
(författare)
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Few-cycle lightwave-driven currents in a semiconductor at high repetition rate
- 2020
-
Ingår i: Optica. - 2334-2536. ; 7:4, s. 276-279
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Tidskriftsartikel (refereegranskat)abstract
- When an intense, few-cycle light pulse impinges on a dielectric or semiconductor material, the electric field will interact nonlinearly with the solid, driving a coherent current. An asymmetry of the ultrashort, carrier-envelope-phase-stable waveform results in a net transfer of charge, which can be measured by macroscopic electric contact leads. This effect has been pioneered with extremely short, single-cycle laser pulses at low repetition rate, thus limiting the applicability of its potential for ultrafast electronics. We investigate lightwave-driven currents in gallium nitride using few-cycle laser pulses of nearly twice the duration and at a repetition rate 2 orders of magnitude higher than in previous work. We successfully simulate our experimental data with a theoretical model based on interfering multiphoton transitions, using the exact laser pulse shape retrieved from dispersion-scan measurements. Substantially increasing the repetition rate and relaxing the constraint on the pulse duration marks an important step forward toward applications of controlling currents with light.
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| 20. |
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| 21. |
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| 22. |
- Mikaelsson, Sara, et al.
(författare)
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A high-repetition rate attosecond light source for time-resolved coincidence spectroscopy
- 2020
-
Ingår i: Nanophotonics. - : Walter de Gruyter GmbH. - 2192-8614 .- 2192-8606. ; 10:1, s. 117-128
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Tidskriftsartikel (refereegranskat)abstract
- Attosecond pulses, produced through high-order harmonic generation in gases, have been successfully used for observing ultrafast, subfemtosecond electron dynamics in atoms, molecules and solid state systems. Today's typical attosecond sources, however, are often impaired by their low repetition rate and the resulting insufficient statistics, especially when the number of detectable events per shot is limited. This is the case for experiments, where several reaction products must be detected in coincidence, and for surface science applications where space charge effects compromise spectral and spatial resolution. In this work, we present an attosecond light source operating at 200 kHz, which opens up the exploration of phenomena previously inaccessible to attosecond interferometric and spectroscopic techniques. Key to our approach is the combination of a high-repetition rate, few-cycle laser source, a specially designed gas target for efficient high harmonic generation, a passively and actively stabilized pump-probe interferometer and an advanced 3D photoelectron/ion momentum detector. While most experiments in the field of attosecond science so far have been performed with either single attosecond pulses or long trains of pulses, we explore the hitherto mostly overlooked intermediate regime with short trains consisting of only a few attosecond pulses. We also present the first coincidence measurement of single-photon double-ionization of helium with full angular resolution, using an attosecond source. This opens up for future studies of the dynamic evolution of strongly correlated electrons.
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| 23. |
- Mikaelsson, Sara, et al.
(författare)
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A high-repetition rate attosecond light source for time-resolved coincidence spectroscopy
- 2021
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Ingår i: Frontiers in Optics and Photonics. - : De Gruyter. - 9783110710687 - 9783110709735 ; , s. 119-130
-
Bokkapitel (refereegranskat)abstract
- Attosecond pulses, produced through high-order harmonic generation in gases, have been successfully used for observing ultrafast, subfemtosecond electron dynamics in atoms, molecules and solid state systems. Today's typical attosecond sources, however, are often impaired by their low repetition rate and the resulting insufficient statistics, especially when the number of detectable events per shot is limited. This is the case for experiments, where several reaction products must be detected in coincidence, and for surface science applications where space charge effects compromise spectral and spatial resolution. In this work, we present an attosecond light source operating at 200 kHz, which opens up the exploration of phenomena previously inaccessible to attosecond interferometric and spectroscopic techniques. Key to our approach is the combination of a high-repetition rate, few-cycle laser source, a specially designed gas target for efficient high harmonic generation, a passively and actively stabilized pump-probe interferometer and an advanced 3D photoelectron/ion momentum detector. While most experiments in the field of attosecond science so far have been performed with either single attosecond pulses or long trains of pulses, we explore the hitherto mostly overlooked intermediate regime with short trains consisting of only a few attosecond pulses. We also present the first coincidence measurement of single-photon dou-ble-ionization of helium with full angular resolution, using an attosecond source. This opens up for future studies of the dynamic evolution of strongly correlated electrons.
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| 24. |
- Mikaelsson, Sara, et al.
(författare)
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Controlled asymmetric photoelectron emission using electron wavepacket interference
- 2019
-
Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. - 9781728104690
-
Konferensbidrag (refereegranskat)abstract
- Two-color ionization is a powerful method for characterizing light fields and investigating atomic and molecular physics with attosecond sources based on High Harmonic Generation (HHG). Depending on the time duration of the light fields, two main techniques have been established: streaking [1], appropriate in the regime where a single attosecond pulse is generated, and RABBIT, used instead when a relatively long fundamental pulse generates an XUV pulse train and the variation between consecutive XUV pulses is negligible [2]. In the regime where high harmonics are generated by a few-cycle fundamental pulse, however, both the amplitude and phase of the few resulting XUV pulses vary significantly, and this variation can be controlled by the CEP of the driving IR field [3]. In this work, we use attosecond pulse trains produced by HHG in argon using a 200 kHz-repetition rate, Carrier-Envelope-Phase (CEP) stable, 6-fs OPCPA laser system [4] and detect emitted photoelectrons from helium byby a three-dimensional (3D) momentum spectrometer [5]. With our excitation scheme, where a weak replica of the generating IR is overlapped with the short XUV pulse train for photoionization, we investigate the regime between the two limits represented by streaking and RABBIT.
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| 25. |
- Mikaelsson, Sara, et al.
(författare)
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Spatio-temporal characterization and optimization of a 200-kHz OPCPA laser system
- 2018
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Ingår i: CLEO : Science and Innovations, CLEO_SI 2018 - Science and Innovations, CLEO_SI 2018. - 9781557528209 ; Part F94-CLEO_SI 2018
-
Konferensbidrag (refereegranskat)abstract
- We present measurements on a few cycle OPCPA laser chain where due to careful characterization and compensation of the spectral phase and spatio-temporal couplings, we are able achieve efficient HHG with very low pulse energy.
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| 26. |
- Miranda, Miguel, et al.
(författare)
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Measurement and correction of spectral phase in a few-cycle parametric amplifier
- 2018
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Ingår i: Ultrafast Optics 2017 : Abstract Book - Abstract Book. - 0277-786X .- 1996-756X. - 9781510617162 ; 10606, s. 75-75
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Konferensbidrag (refereegranskat)abstract
- We study the spectral phase introduced by parametric amplification and how high extraction efficiency of energy leads to deterioration of the phase. Avoiding this regime, and using a pulse shaper, we achieve high-contrast ultrashort pulses.
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| 27. |
- Neoričić, Lana, et al.
(författare)
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4D spatio-temporal electric field characterization of ultrashort light pulses undergoing filamentation
- 2022
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Ingår i: Optics Express. - 1094-4087. ; 30:15, s. 27938-27950
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental method capable of capturing the complete spatiotemporal dynamics of filamenting ultrashort laser pulses. By employing spatially resolved Fourier transform spectrometry in combination with the capability to terminate the filament at any length, we can follow the nonlinear dynamics in four dimensions, i.e. the transverse domain, time and filament length. Our method thus not only enables the full characterization of the filamentation process throughout its evolution, but also allows to identify and select laser pulses with desired parameters.
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| 28. |
- Stegmayr, Bernd, et al.
(författare)
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Low-dose atorvastatin in severe chronic kidney disease patients : a randomized, controlled endpoint study
- 2005
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Ingår i: Scandinavian Journal of Urology and Nephrology. - 0036-5599 .- 1651-2065. ; 39:6, s. 489-497
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Tidskriftsartikel (refereegranskat)abstract
- Objective. There have been no endpoint studies with statins for patients with severe renal failure. The purpose of this prospective, open, randomized, controlled study was to investigate whether atorvastatin (10 mg/day) would alter cardiovascular endpoints and the overall mortality rate of patients with chronic kidney disease stage 4 or 5 (creatinine clearance < 30 ml/min).Material and methods. The study subjects comprised 143 patients who were randomized either to placebo (controls; n=73; mean age 69.5 years) or to treatment with atorvastatin (n=70; mean age 67.9 years). The patients included were either non-dialysis (n=33), haemodialysis (n=97) or peritoneal dialysis (n=13) patients. Analysis focused on the primary endpoints of all-cause mortality, non-lethal acute myocardial infarction, coronary artery bypass graft surgery and percutaneous transluminal coronary angioplasty. Statistical analysis for endpoint data was mainly by intention-to-treat.Results. Primary endpoints occurred in 74% of the subjects. There was no difference in outcome between the control and atorvastatin groups. The 5-year endpoint-free survival rate from study entry was 20%. Atorvastatin was withdrawn in 20% of patients due to unacceptable side-effects. In the atorvastatin group, low-density lipoprotein (LDL) cholesterol was reduced by 35% at 1 month and then sustained. The controls showed a progressive reduction in LDL cholesterol until 36 months.Conclusions. Although atorvastatin reduced total and LDL cholesterol effectively it was not beneficial regarding the long-term outcomes of cardiovascular endpoints or survival. In contrast to other patient groups, patients with severe chronic kidney disease, especially those on dialysis, seem to derive limited benefit from this lower dose of atorvastatin.
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| 29. |
- Sytcevich, Ivan, et al.
(författare)
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Characterizing ultrashort laser pulses with second harmonic dispersion scans
- 2021
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Ingår i: Journal of the Optical Society of America B: Optical Physics. - 0740-3224. ; 38:5, s. 1546-1555
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Forskningsöversikt (refereegranskat)abstract
- The dispersion scan (d-scan) technique has emerged as a simple-to-implement characterization method for ultrashort laser pulses. D-scan traces are intuitive to interpret and retrieval algorithms that are both fast and robust have been developed to obtain the spectral phase and the temporal pulse profile. Here, we shortly review the second harmonic generation d-scan technique, focusing predominantly on results obtained at the Lund Laser Centre.We describe and compare recent implementations for the characterization of few- and multi-cycle pulses as well as two different approaches for recording d-scan traces in a single shot, thus showing the versatility of the technique.
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| 30. |
- Sytcevich, Ivan, et al.
(författare)
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Compact single-shot D-scan setup for the characterization of few-cycle laser pulses
- 2019
-
Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. - 9781728104690
-
Konferensbidrag (refereegranskat)abstract
- Ultrashort laser pulses have become an indispensable tool in physics, chemistry and engineering. Their numerous applications call for accurate and robust characterization techniques able to reliably retrieve the pulse's intensity profile. Different methods, such as FROG [1] or SPIDER [2] and their variants, have been developed in past decades and are now common in many laboratories. More novel approaches based on manipulating the light's spectral phase include techniques like MIIPS [3] and dispersion scan (d-scan) [4].
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| 31. |
- Vogelsang, Jan, et al.
(författare)
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Coherent Excitation and Control of Plasmons on Gold Using Two-Dimensional Transition Metal Dichalcogenides
- 2021
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 8:6, s. 1607-1615
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Tidskriftsartikel (refereegranskat)abstract
- The hybrid combination of two-dimensional (2D) transition metal dichalcogenides (TMDs) and plasmonic materials open up novel means of (ultrafast) optoelectronic applications and manipulation of nanoscale light-matter interaction. However, control of the plasmonic excitations by TMDs themselves has not been investigated. Here, we show that the ultrathin 2D WSe2 crystallites permit nanoscale spatially controlled coherent excitation of surface plasmon polaritons (SPPs) on smooth Au films. The resulting complex plasmonic interference patterns are recorded with nanoscale resolution in a photoemission electron microscope. Modeling shows good agreement with experiments and further indicates how SPPs can be tailored with high spatiotemporal precision using the shape of the 2D TMDs with thicknesses down to single molecular layers. We demonstrate the use of WSe2 nanocrystals as 2D optical elements for exploring the ultrafast dynamics of SPPs. Using few-femtosecond laser pulse pairs we excite an SPP at the boundary of a WSe2 crystal and then have a WSe2 monolayer wedge act as a delay line inducing a spatially varying phase difference down to the attosecond time range. The observed effects are a natural yet unexplored consequence of high dielectric functional values of TMDs in the visible range that should be considered when designing metal-TMD hybrid devices. As the 2D TMD crystals are stable in air, can be defect free, can be synthesized in many shapes, and are reliably positioned on metal surfaces, using them to excite and steer SPPs adds an interesting alternative in designing hybrid structures for plasmonic control.
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| 32. |
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