| 1. |
- Ferri, Julien, 1990, et al.
(författare)
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Enhancement of laser-driven ion acceleration in non-periodic nanostructured targets
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:1
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Tidskriftsartikel (refereegranskat)abstract
- Using particle-in-cell simulations, we demonstrate an improvement of the target-normal-sheath acceleration (TNSA) of protons in non-periodically nanostructured targets with micron-scale thickness. Compared to standard flat foils, an increase in the proton cutoff energy by up to a factor of two is observed in foils coated with nanocones or perforated with nanoholes. The latter nano-perforated foils yield the highest enhancement, which we show to be robust over a broad range of foil thicknesses and hole diameters. The improvement of TNSA performance results from more efficient hot-electron generation, caused by a more complex laser-electron interaction geometry and increased effective interaction area and duration. We show that TNSA is optimized for a nanohole distribution of relatively low areal density and that is not required to be periodic, thus relaxing the manufacturing constraints.
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| 2. |
- Migal, E. A., et al.
(författare)
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Role of deposited energy density and impact ionization in the processes of femtosecond laser-matter interaction in solids: scaling from visible to mid-IR
- 2019
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Ingår i: Nonlinear Optics and Applications XI. Proceedings Vol. 11026. SPIE OPTICS + OPTOELECTRONICS, 1-4 April 2019. - : SPIE. - 9781510627192
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Konferensbidrag (refereegranskat)abstract
- The deposited energy density (DED) serves as a key parameter in the process of the femtosecond laser pulse energy delivery into the bulk of transparent dielectrics. The laser-induced micromodification can be created if the value of DED exceeds a certain threshold, which is specific for each material and does not depend on the laser wavelength. In this contribution, we present a comprehensive study of the DED evolution with the driving pulse energy and wavelength under femtosecond microstructuring of transparent dielectrics. To precisely determine the laser impact area we applied for the first time a real-time diagnostic of microplasma based on third harmonic generation. This technique gives submicron spatial resolution and is extremely sensitive to the free electron density (about 10(-5) of the critical electron density). We found out that the threshold DED equals to approximately 2.5 kJ/cm(3) for fused silica and roughly corresponds to excess of glass transition temperature. The highest DED is achieved for the shortest wavelength (620 nm) and equals to 16 kJ/cm(3).
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| 3. |
- Smetanina, E., et al.
(författare)
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Light bullets from chirped high-power femtosecond pulses under normal GVD for Mid-IR optical parametric amplification
- 2019
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Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. - 9781557528209
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Konferensbidrag (refereegranskat)abstract
- Mid-IR laser systems have a variety of applications ranging from generation of coherent x-ray and THz radiation to microstructuring of bulk dielectrics and semiconductors. To reach the mid-IR region, optical parametric amplifiers (OPAs) are employed for down-conversion of high energy near-IR pump lasers and require seed radiation at 1.5-2 μm. Several attempts have been made to improve the supercontinuum (SC) generated in bulk [1,2] and gas [3], but the spectral brightness and/or temporal quality in the region of 1.5-2 μm stays quite poor. We performed an extensive parametric analysis of SC generation in different dielectric materials and found a regime with well-resolved local maxima in the red wing that is highly appropriate as an OPA seed. These results provide strong ground for further development of SC-seeded ultrafast OPAs in the mid-IR spectral range using Cr:Forsterite and ytterbium based lasers as pump sources [4].
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| 4. |
- Martínez, P. González De Alaiza, et al.
(författare)
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Modeling the time-dependent electron dynamics in dielectric materials induced by two-color femtosecond laser pulses: Applications to material modifications
- 2021
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Ingår i: Physical Review A. - 2469-9934 .- 2469-9926. ; 103:3
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Tidskriftsartikel (refereegranskat)abstract
- Controlling the electron dynamics during laser-matter interactions is a key factor to control the energy deposition and subsequent material modifications induced by femtosecond laser pulses. One way to achieve this goal is to use two-color femtosecond laser pulses. In this paper, the electron dynamics in dielectric materials induced by two-color femtosecond laser pulses is studied by solving dedicated optical Bloch equations. This model includes photo- and impact ionization, the laser heating of conduction electrons, their recombination to the valence band, and their collisions with phonons. The influence of photon energies, laser intensities, and pulse-to-pulse delay is analyzed. Depending on the interaction process, colors cooperate to excite electrons or drive them independently. For the given laser parameters, an optimal pulse-to-pulse delay is found which enhances significantly the energy deposition into the material, in agreement with experimental observations.
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| 5. |
- Potemkin, F. V., et al.
(författare)
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Influence of wave-front curvature on supercontinuum energy during filamentation of femtosecond laser pulses in water
- 2018
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 97:3
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that using spatially divergent incident femtosecond 1240-nm laser pulses in water leads to an efficient supercontinuum generation in filaments. Optimal conditions were found when the focal plane is placed 100-400 mu m before the water surface. Under sufficiently weak focusing conditions [numerical aperture (NA) < 0.2] and low-energy laser pulses, the supercontinuum energy generated in divergent beams is higher than the supercontinuum energy generated in convergent beams. Analysis by means of the unidirectional pulse propagation equation shows a dramatic difference between filamentation scenarios of divergent and convergent beams, that explains corresponding features of the supercontinuum generation. Under strong focusing conditions (NA >= 0.2) and high-energy laser pulses, the supercontinuum generation is suppressed for convergent beams in contrast to divergent beams that nevertheless are shown experimentally to allow supercontinuum generation. The presented technique of the supercontinuum generation in divergent beams in water is highly demanded in a development of femtosecond optical parametric amplifiers.
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| 6. |
- Smetanina, E., et al.
(författare)
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Modeling femtosecond laser-induced electron dynamics in dielectrics by means of optical bloch equations
- 2019
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Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. - 9781557528209
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Konferensbidrag (refereegranskat)abstract
- Modern laser technologies provide high-intensity single- or few-cycle laser pulses which open new doors to study laser-matter interaction processes. To predict new routes towards their active control, advanced theoretical and numerical models are required. When approaching the highly non-linear interaction regimes close to the material damage threshold, the traditional perturbation expansion of the polarization response is not valid anymore and a quantum-mechanical modeling is essential [1-4]. A good candidate to model the electron dynamics within this framework is the Optical Bloch Equations (OBEs) approach, which provides all-order material response within a single self-consistent description. We develop a new OBEs-based model of laser matter-interaction including field-induced ionization, both linear and nonlinear polarization responses leading to high harmonics, impact ionization and various relaxation processes taking place in dielectric materials. Here, we apply our model to describe the electron dynamics induced by an intense femtosecond laser pulse in a dielectric.
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| 7. |
- Smetanina, E., et al.
(författare)
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Optical Bloch modeling of femtosecond-laser-induced electron dynamics in dielectrics
- 2020
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Ingår i: Physical Review E - Statistical, Nonlinear, and Soft Matter Physics. - 2470-0053 .- 2470-0045. ; 101:6
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Tidskriftsartikel (refereegranskat)abstract
- A model based on optical Bloch equations is developed to describe the interaction of femtosecond laser pulses with dielectric solids, accounting for optical-cycle-resolved electron dynamics. It includes the main physical processes at play: photoionization, impact ionization, direct and collisional laser heating, and recombination. By using an electron band structure, this approach also accounts for material optical properties as nonlinear polarization response. Various studies are performed, shedding light on the contribution of various processes to the full electron dynamics depending on laser intensity and wavelength. In particular, the standard influence of the impact ionization process is retrieved.
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| 8. |
- Smetanina, N., et al.
(författare)
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Prevalence of overweight/obesity in relation to dietary habits and lifestyle among 7-17 years old children and adolescents in Lithuania
- 2015
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Ingår i: Bmc Public Health. - : Springer Science and Business Media LLC. - 1471-2458. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Background: Until recently increasing prevalence of overweight and obesity among pediatric population in Europe and worldwide contributes to major well-known risks for metabolic consequences in later life. The aim of this study was to determine the prevalence of overweight/obesity among children and adolescents in Lithuania and assess its association with energy balance related behaviors as well as familial demographic and socioeconomic factors. Methods: Cross-sectional study included 3990 7-17 years old schoolchildren from 40 schools of Kaunas region, Lithuania. Study participants underwent anthropometric measurements. Body mass index (BMI) was evaluated according to International Obesity Task Force (IOTF) criteria for children and adolescents. Children and adolescents and their parents filled in the questionnaires on parental sociodemographic characteristics, dietary habits, TV watching time, and family socioeconomic status. Results: The prevalence of underweight, overweight, and obesity among boys and girls was 6.9 and 11.7 % (P < 0.05), 12.6 and 12.6 % (P > 0.05), and 4.9 and 3.4 % (P < 0.05), respectively. Obesity was significantly more prevalent in the 7-9 years old group (6.7 and 4.8 % in boys and girls, respectively, P < 0.05). Lower meals frequency and breakfast skipping were directly associated with overweight/obesity (P < 0.05); however, physical inactivity was not associated with higher BMI. Children's overweight/obesity was directly associated with lower paternal education and unemployment (OR 1.30, P = 0.013 and OR 1.56, P = 0.003, respectively). Conclusions: The prevalence of overweight and obesity among 7-17 years old Lithuanian children and adolescents was more prevalent in younger age, still being one of the lowest across the European countries. Meals frequency, breakfast skipping, paternal education and unemployment as well as a family history of arterial hypertension were found to be associated with children's and adolescents' overweight/obesity.
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| 9. |
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| 10. |
- Thiele, Illia, 1989, et al.
(författare)
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Terahertz emission from laser-driven gas plasmas: A plasmonic point of view
- 2018
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Ingår i: Optica. - 2334-2536. ; 5:12, s. 1617-1622
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Tidskriftsartikel (refereegranskat)abstract
- We disclose an unanticipated link between plasmonics and nonlinear frequency down-conversion in laser-induced gas-plasmas. For two-color femtosecond pump pulses, a plasmonic resonance is shown to broaden the terahertz emission spectra significantly. We identify the resonance as a leaky mode, which contributes to the emission spectra whenever electrons are excited along a direction where the plasma size is smaller than the plasma wavelength. As a direct consequence, such resonances can be controlled by changing the polarization properties of elliptically shaped driving laser pulses. Both experimental results and 3D Maxwell consistent simulations confirm that a significant terahertz pulse shortening and spectral broadening can be achieved by exploiting the transverse driving laser beam shape as an additional degree of freedom.
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