| 1. |
- Bergé, Luc, et al.
(författare)
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THz emissions by two-color filaments in air: Revisiting the wavelength scaling
- 2019
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Ingår i: Optics InfoBase Conference Papers. - 2162-2701. ; Part F134-NLO 2019
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Konferensbidrag (refereegranskat)abstract
- We report impressive growths in the terahertz energies supplied by air plasmas created by two-color laser pulses whose fundamental wavelength is increased. Comprehensive 3D simulations reveal the crucial role of the two-color relative phase.
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| 2. |
- Bergé, Luc, et al.
(författare)
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Wavelength scaling of THz emissions by two-color filaments in air
- 2019
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Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. ; June 2019
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Konferensbidrag (refereegranskat)abstract
- Producing terahertz (THz) radiation by ultrashort laser pulses has become an active field of research because of its promising applications in, e.g., spectroscopy and medical imaging [1]. Efficient THz emitters can be obtained by focusing into air a two-color femtosecond light pulse, composed of fundamental (FH) and second (SH) harmonics, in order to create a plasma channel that acts as a frequency converter [2]. Recent studies [3,4] showed that increasing the pump wavelength enhances the THz energy. However, there is no consensus on the gain factors expected when pushing the FH wavelength, λ0, from the near-IR to the mid-IR range. Clerici et al. [3] reported THz energy yields scaling like λ20 in the range 0.8-1.8 μm. By contrast, according to the local-current model [2,4], the largest THz energy attained by two colors with π/2 relative phase should follow a scaling in λ20 only.
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| 3. |
- 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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| 4. |
- González De Alaiza Martínez, Pedro, et al.
(författare)
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Maxwell-consistent, symmetry- and energy-preserving solutions for ultrashort-laser-pulse propagation beyond the paraxial approximation
- 2018
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Ingår i: Physical Review A. - 2469-9934 .- 2469-9926. ; 98:4
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Tidskriftsartikel (refereegranskat)abstract
- We analytically and numerically investigate the propagation of ultrashort tightly focused laser pulses in vacuum, with particular emphasis on Hermite-Gaussian and Laguerre-Gaussian modes. We revisit the Lax series approach for forward-propagating linearly polarized laser pulses, to obtain Maxwell-consistent and symmetry-preserving analytical solutions for the propagation of all field components beyond the paraxial approximation in four-dimensional geometry (space and time). We demonstrate that our solution conserves the energy, which is set by the paraxial-level term of the series. The full solution of the wave equation towards which our series converges is calculated in the Fourier space. Three-dimensional numerical simulations of ultrashort tightly focused pulses validate our analytical development.
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| 5. |
- Ivanov, Maksym, et al.
(författare)
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Intensity modulated terahertz vortex wave generation in air plasma by two-color femtosecond laser pulses
- 2019
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 44:15, s. 3889-3892
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the generation of broadband terahertz (THz) pulses with phase singularity from air plasmas created by fundamental and second harmonic laser pulses. We show that when the second harmonic beam carries a vortex charge, the THz beam acquires a vortex structure as well. A generic feature of this THz vortex is that the intensity is modulated along the azimuthal angle, which can be attributed to the spatially varying relative phase difference between the two pump harmonics. Fully space- and time-resolved numerical simulations reveal that transverse instabilities of the pump further affect the emitted THz field along nonlinear propagation, which may produce additional singularities resulting in a rich vortex structure. The predicted intensity modulation is experimentally demonstrated with a thermal camera, in excellent agreement with simulation results. The presence of phase singularities in the experiment is revealed by astigmatic transformation of the beam using a cylindrical mirror. (c) 2019 Optical Society of America
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| 6. |
- Ivanov, Maksym, 1990, et al.
(författare)
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Terahertz wave generation in air by femtosecond optical vortex 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. - 9781557528209
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Konferensbidrag (refereegranskat)abstract
- Terahertz (THz) radiation is of great current interest due to many applications such as nonlinear THz spectroscopy and imaging. One of the compact and effective methods to obtain very high THz field strengths and extremely broadband spectral widths is THz wave generation from plasma filaments formed in air by focused bichromatic femtosecond laser pulses consisting of the first and the second harmonics (FH, SH). Here we investigate the effect of an azimuthal phase modulation of the SH carrying an optical vortex charge on the intensity and phase distribution of the THz pulse emitted from the laser induced plasma filament in air. We present both experimental and theoretical results. © 2019 IEEE.
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| 7. |
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| 8. |
- Kaltenecker, K. J., et al.
(författare)
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Plasmonic Resonances Affecting Terahertz Generation in Laser-Induced Gas-Plasmas
- 2018
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Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - : Book Series: International Conference on Infrared Millimeter and Terahertz Waves. - 2162-2027 .- 2162-2035. ; 2018-September
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Konferensbidrag (refereegranskat)abstract
- We demonstrate that plasmonic resonances can be used to broaden the terahertz emission spectrum from two-color laser-driven gas-plasmas. This effect can be controlled by changing the polarization properties of elliptically shaped driving laser-pulses.
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| 9. |
- 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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| 10. |
- Nguyen, Alisée, et al.
(författare)
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Broadband terahertz radiation from two-color mid- and far-infrared laser filaments in air
- 2018
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Ingår i: Physical Review A. - 2469-9934 .- 2469-9926. ; 97:6
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Tidskriftsartikel (refereegranskat)abstract
- We study terahertz (THz) emission by two-color femtosecond filaments in air using pump wavelengths λ0 from 0.8 to 10.6 μm. Comprehensive three-dimensional numerical simulations show that tens-of-centimeter long filaments created by a 10.6-μm pump pulse can produce mJ energy yields and GV/m field strengths, while the laser-to-THz conversion efficiency exceeds the percent level. Changing temperature and humidity conditions reveals a surprisingly high stability of the THz spectra against different weather conditions. We also examine the role of many-body Coulomb effects on ionization. This additional plasma source promotes longer filaments that act as efficient THz emitters, despite enhanced plasma defocusing.
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