| 1. |
- Miranda, Miguel, et al.
(författare)
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All-optical measurement of the complete waveform of octave-spanning ultrashort light pulses
- 2019
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Ingår i: Optics Letters. - 0146-9592. ; 44:2, s. 191-194
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the complete temporal characterization of the optical waveform of visible near-infrared octave-spanning ultrashort laser pulses, using an all-optical, all-solid-state, and fully inline dispersion-scan device based only on second-harmonic generation.
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| 2. |
- Alonso, Benjamin, et al.
(författare)
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Characterization of sub-two-cycle pulses from a hollow-core fiber compressor in the spatiotemporal and spatiospectral domains
- 2013
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 112:1, s. 105-114
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Tidskriftsartikel (refereegranskat)abstract
- We have post-compressed 25 fs (Fourier limit) amplified pulses in an argon-filled hollow-core fiber. The output pulses were compressed using a pair of wedges and chirped mirrors down to 4.5 fs (Fourier limit of 4.1 fs), which corresponds to less than two optical cycles. We then performed the characterization of the pulses by combining the d-scan and the STARFISH techniques. The temporal (and spectral) measurement of the pulses is done with d-scan, which is used as the reference to extend the characterization to the spatiotemporal (and spatiospectral) amplitude and phase of the pulses by means of STARFISH. The post-compressed pulses at the output of the hollow-fiber had an energy of 150 mu J. The analysis of the pulses revealed larger spectral broadening and blue-shift, and shorter duration at the center of the beam. For the first time, we demonstrate the complete characterization of intense ultra-broadband pulses in the sub-two-cycle regime, which provides an improved insight into the properties (space-time and space-frequency) of the pulses and is highly relevant for their applications.
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| 3. |
- Dahlstrand, Christian
(författare)
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Ground and Excited State Aromaticity : Design Tools for π-Conjugated Functional Molecules and Materials
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main focus of this thesis is on the aromaticity of the ground state and electronically excited states of π-conjugated molecules and polymers, as well as how aromaticity is connected to their properties.The electronic structures of polybenzenoid hydrocarbons (PBHs) were explored through density functional theory (DFT) calculations and the π-component of the electron localization function (ELFπ). The study revealed how the π-electronic structure is influenced by the fusion of double bonds or benzene rings to the PBHs. We also demonstrated that the π-electrons of benzene extend to accommodate as much aromaticity as possible when bond length distorted. The aromatic chameleon property displayed by fulvenes, isobenzofulvenes, fulvalenes, bis(fulvene)s, and polyfulvenes were investigated using DFT calculations. The tria-, penta-, and heptafulvenes were shown to possess ionization energies and electron affinities which can be tuned extensively by substitution, some of which even outperform TTF and TCNQ, the prototypical electron donor and acceptor, respectively. The singlet-triplet energy gap of pentafulvenes can be tuned extensively by substitution to the point that the triplet state is lower than the singlet state and thus becomes the ground state. The ELFπ of isobenzofulvene shows that the benzene ring in an electronically excited state can be more aromatic than the corresponding ring in the ground state. We have shown that the 6-ring of [5.6.7]quinarene is influenced by a Hückel aromatic resonance structure with 4n+2 π-electrons in the excited quintet state. The bis(fulvene)s which are composed of a donor type heptafulvene and an acceptor type pentafulvene, retain the basic donor-acceptor properties of the two fragments and could function as compact donor-acceptor dyads. A few of the designed polyfulvenes were found to have band gaps below 1 eV at the PBC-B3LYP/6-31G(d) level.Various 2,7-disubstituted fluorenones and dibenzofulvenes were synthesized and their excited state properties were investigated by absorption spectroscopy and time-dependent DFT calculations. It was found that the 1A → 1B transition of ππ* character can be tuned by substitution in the 2,7-positions. The 2,7-bis(N,N-dimethyl) derivatives of fluorenone and dibenzofulvene displayed low energy transitions at 2.18 and 1.61 eV, respectively, in toluene.
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| 4. |
- Hernandez-Garcia, C., et al.
(författare)
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Carrier-envelope-phase insensitivity in high-order harmonic generation driven by few-cycle laser pulses
- 2015
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Ingår i: Optics Express. - 1094-4087. ; 23:16, s. 21497-21508
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Tidskriftsartikel (refereegranskat)abstract
- We present evidence for self-stabilization of the relative spectral phase of high-order harmonic emission against intensity variations of the driving field. Our results demonstrate that, near the laser focus, phase matching of the harmonic field from a macroscopic target can compensate for the intensity dependence of the intrinsic phase of the harmonics emitted by a single radiator. As a consequence, we show experimentally and theoretically the insensitivity of the harmonic spectra produced at the laser focus against variations of the carrier-envelope phase (CEP) of a sub-two-cycle driving field. In addition, the associated attosecond pulse trains exhibit phase locking against CEP changes of the few-cycle driver. (C) 2015 Optical Society of America
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| 5. |
- Holgado, W., et al.
(författare)
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Continuous spectra in high-harmonic generation driven by multicycle laser pulses
- 2016
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 93:1
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Tidskriftsartikel (refereegranskat)abstract
- We present observations of the emission of XUV continua in the 20-37-eV region by high-harmonic generation with 4-7-fs pulses focused onto a Kr gas jet. The underlying mechanism relies on coherent control of the relative delays and phases between individually generated attosecond pulses, achievable by adjusting the chirp of the driving pulses and the interaction geometry. Under adequate negative chirp and phase-matching conditions, the resulting interpulse interference yields a continuum XUV spectrum, which is due to both microscopic and macroscopic (propagation) contributions. This technique opens the route for modifying the phase of individual attosecond pulses and for the coherent synthesis of XUV continua from multicycle driving laser pulses without the need of an isolated attosecond burst.
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| 6. |
- Matxain, Jon M, et al.
(författare)
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New solids based on B12N12 fullerenes
- 2007
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Ingår i: The Journal of Physical Chemistry C. - Washington, DC : American Chemical Society. - 1932-7447 .- 1932-7455. ; 111:36, s. 13354-60
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, BN fullerenes have been synthesized experimentally. As their carbon counterparts, these BN fullerenes could be assembled in molecular solids, but this possibility has been studied little in the literature. In this work, we focus on the smallest synthesized BN fullerene, B12N12, which is built by squares and hexagons. First, the interaction between two of these fullerenes has been analyzed, using the hybrid B3LYP and MPW1PW91 density functional methods. Two different interactions have been studied in the dimer, a square facing a square (S−S) and a hexagon facing a hexagon (H−H). In both cases, a B is facing a N. The most stable dimer was found to be S−S facing, with covalent interactions between the monomers, but other dimers with weak interactions have been found as well, which opens possibilities of new systems, as in the case of fullerene dimers and solids. The solids resulting from the infinite repetition of the characterized dimers were optimized, finding two different solids, with covalent and weak interactions between monomers, respectively. The solid with covalent interactions is a nanoporous material that is more stable by around 12 eV. Because of the nanoporous character of this solid, it could be used for heterogeneous catalysis, molecular transport, and so forth. The SIESTA code with the GGA-PBE density functional method has been used for the solid-state calculations.
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| 7. |
- Pinto, Ana Margarida, et al.
(författare)
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Emotion regulation and the salience network : a hypothetical integrative model of fibromyalgia
- 2023
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Ingår i: Nature Reviews Rheumatology. - : Springer Nature. - 1759-4790 .- 1759-4804. ; 19:1, s. 44-60
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Tidskriftsartikel (refereegranskat)abstract
- Fibromyalgia is characterized by widespread pain, fatigue, sleep disturbances and other symptoms, and has a substantial socioeconomic impact. Current biomedical and psychosocial treatments are unsatisfactory for many patients, and treatment progress has been hindered by the lack of a clear understanding of the pathogenesis of fibromyalgia. We present here a model of fibromyalgia that integrates current psychosocial and neurophysiological observations. We propose that an imbalance in emotion regulation, reflected by an overactive 'threat' system and underactive 'soothing' system, might keep the 'salience network' (also known as the midcingulo-insular network) in continuous alert mode, and this hyperactivation, in conjunction with other mechanisms, contributes to fibromyalgia. This proposed integrative model, which we term the Fibromyalgia: Imbalance of Threat and Soothing Systems (FITSS) model, should be viewed as a working hypothesis with limited supporting evidence available. We hope, however, that this model will shed new light on existing psychosocial and biological observations, and inspire future research to address the many gaps in our knowledge about fibromyalgia, ultimately stimulating the development of novel therapeutic interventions.
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| 8. |
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| 9. |
- Silva, Francisco, et al.
(författare)
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Monolithic single-shot dispersion-scan : A new tool for real-time measurement and optimization of femtosecond pulses
- 2017
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Ingår i: The European Conference on Lasers and Electro-Optics, CLEO_Europe 2017. - 9781509067367
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Konferensbidrag (refereegranskat)abstract
- The precise characterization of femtosecond laser pulses is as challenging as their generation and a topic of intense research. Dispersion-scan (d-scan) [1] is a recently established technique where the spectrum of a nonlinear signal, e.g., second-harmonic generation (SHG), is measured as a function of dispersion applied to the pulse. The spectral phase of the pulse can then be retrieved from the resulting 2D trace using an iterative algorithm. An important implementation of d-scan, based on a chirped mirror and wedge compressor, involves progressively moving one of the wedges around the maximum compression point and acquiring the resulting SHG spectrum for each insertion with a standard spectrometer. This robust and fully inline approach, which does not require any beamsplitting or temporal delays, has enabled the simultaneous compression and measurement of pulses down to single-cycle durations [2-4], but its scanning nature precludes single-shot operation. A single-shot d-scan variant that explores the spatially dependent dispersion of a glass prism was successfully demonstrated with 3.2 fs pulses [5], but the relatively small amount of dispersion that can be introduced by a single prism limits its use to few-cycle pulses.
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| 10. |
- 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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