| 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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| 11. |
- Nguyen, Alisée, et al.
(författare)
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Wavelength scaling of terahertz pulse energies delivered by two-color air plasmas
- 2019
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 44:6, s. 1488-1491
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Tidskriftsartikel (refereegranskat)abstract
- We address the long-standing problem of anomalous growth observed in the terahertz (THz) energy yield from air plasmas created by two-color laser pulses, as the fundamental wavelength λ 0 is increased. Using two distinct optical parametric amplifiers (OPAs), we report THz energies scaling like λ α0 with large exponents 5.6 ≤ α ≤ 14.3, which departs from the growth in λ 20 expected from photocurrent theory. By means of comprehensive 3D simulations, we demonstrate that the changes in the laser beam size, pulse duration, and phase-matching conditions in the second-harmonic generation process when tuning the OPA’s carrier wavelength can lead to these high scaling powers. The value of the phase angle between the two colors reached at the exit of the doubling crystal turns out to be crucial and even explains non-monotonic behaviors in the measurements.
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| 12. |
- Nuter, R., et al.
(författare)
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Gain of electron orbital angular momentum in a direct laser acceleration process
- 2020
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Ingår i: Physical Review E. - 2470-0045 .- 2470-0053. ; 101:5
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Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional "particle in cell" simulations show that a quasistatic magnetic field can be generated in a plasma irradiated by a linearly polarized Laguerre-Gauss beam with a nonzero orbital angular momentum (OAM). Perturbative analysis of the electron dynamics in the low intensity limit and detailed numerical analysis predict a laser to electrons OAM transfer. Plasma electrons gain angular velocity thanks to the dephasing process induced by the combined action of the ponderomotive force and the laser induced-radial oscillation Similar to the "direct laser acceleration," where Gaussian laser beams transmit part of its axial momentum to electrons, Laguerre-Gaussian beams transfer a part of their orbital angular momentum to electrons through the dephasing process.
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| 13. |
- Nuter, R., et al.
(författare)
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Plasma solenoid driven by a laser beam carrying an orbital angular momentum
- 2018
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Ingår i: Physical Review E. - 2470-0045 .- 2470-0053. ; 98:3
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Tidskriftsartikel (refereegranskat)abstract
- A megagauss quasistatic axial magnetic field can be produced from the interaction of an intense laser beam carrying an orbital angular momentum with an underdense plasma. Three-dimensional 'particle in cell" simulations and analytical model demonstrate that orbital angular momentum is irreversibly transferred from a tightly focused radially polarized laser beam to electrons without any dissipative effect. A theoretical model describing the individual interaction of electrons with laser shows that particles gain angular momentum during their radial and longitudinal motion in the laser field. The electron rotation and the generated axial magnetic field survive to the end of the laser-plasma interaction and continue over a long time. The agreement between particle in cell simulations and the simplified model identifies routes to increase the intensity of the solenoidal magnetic field by controlling the laser beam characteristics, such as, for example, the orbital angular momentum and/or the pulse duration.
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| 14. |
- Siminos, E., et al.
(författare)
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Generation of intense isolated CEP-tunable sub-cycle pulses in laser-driven wakes
- 2020
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Ingår i: Optics InfoBase Conference Papers. - 2162-2701.
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Konferensbidrag (refereegranskat)abstract
- We present a scheme which leverages laser-driven wakes in plasmas to produce carrier-envelope-phase tunable sub-cycle pulses with central wavelength ranging from the midinfrared to the ultraviolet and up to few tens of mJ energy.
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| 15. |
- Siminos, Evangelos, 1979, et al.
(författare)
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Laser Wakefield Driven Generation of Isolated Carrier-Envelope-Phase Tunable Intense Subcycle Pulses
- 2021
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 126:4
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Tidskriftsartikel (refereegranskat)abstract
- Sources of intense, ultrashort electromagnetic pulses enable applications such as attosecond pulse generation, control of electron motion in solids, and the observation of reaction dynamics at the electronic level. For such applications, both high intensity and carrier-envelope-phase (CEP) tunability are beneficial, yet hard to obtain with current methods. In this Letter, we present a new scheme for generation of isolated CEP tunable intense subcycle pulses with central frequencies that range from the midinfrared to the ultraviolet. It utilizes an intense laser pulse that drives a wake in a plasma, copropagating with a long-wavelength seed pulse. The moving electron density spike of the wake amplifies the seed and forms a subcycle pulse. Controlling the CEP of the seed pulse or the delay between driver and seed leads to CEP tunability, while frequency tunability can be achieved by adjusting the laser and plasma parameters. Our 2D and 3D particle-in-cell simulations predict laser-to-subcycle-pulse conversion efficiencies up to 1%, resulting in relativistically intense subcycle pulses.
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| 16. |
- Siminos, Evangelos, 1979, et al.
(författare)
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Parametric study of laser wakefield driven generation of intense sub-cycle pulses
- 2022
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 64:3
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Tidskriftsartikel (refereegranskat)abstract
- Intense sub-cycle electromagnetic pulses allow one to drive nonlinear processes in matter with unprecedented levels of control. However, it remains challenging to scale such sources in the relativistic regime. Recently, a scheme that utilizes laser-driven wakes in plasmas to amplify and compress seed laser pulses to produce tunable, carrier-envelope-phase stable, relativistic sub-cycle pulses has been proposed. Here, we present parametric studies of this process using particle-in-cell simulations, showing its robustness over a wide range of experimentally accessible laser-plasma interaction parameters, spanning more than two orders of magnitude of background plasma density. The method is shown to work with different gas-jet profiles, including structured density profiles and is robust over a relatively wide range of driver laser intensities. Our study shows that sub-cycle pulses of up to 10mJ of energy can be produced.
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| 17. |
- 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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| 18. |
- 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
-
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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| 19. |
- 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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| 20. |
- Thiele, Illia, 1989, et al.
(författare)
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Electron Beam Driven Generation of Frequency-Tunable Isolated Relativistic Subcycle Pulses
- 2019
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 122
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 American Physical Society. We propose a novel scheme for frequency-tunable subcycle electromagnetic pulse generation. To this end a pump electron beam is injected into an electromagnetic seed pulse as the latter is reflected by a mirror. The electron beam is shown to be able to amplify the field of the seed pulse while upshifting its central frequency and reducing its number of cycles. We demonstrate the amplification by means of 1D and 2D particle-in-cell simulations. In order to explain and optimize the process, a model based on fluid theory is proposed. We estimate that using currently available electron beams and terahertz pulse sources, our scheme is able to produce millijoule-strong midinfrared subcycle pulses.
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| 21. |
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| 22. |
- 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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| 23. |
- Vaičaitis, Virgilijus, et al.
(författare)
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Generation of broadband THz beams with azimuthally modulated phase and intensity by femtosecond laser pulses in air plasma
- 2019
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - 0277-786X .- 1996-756X. ; 11370, s. 443-444
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Konferensbidrag (refereegranskat)abstract
- We report efficient generation of the broadband terahertz (THz) radiation by bichromatic femtosecond laser pulses with flat phase fronts or with a phase singularity focused in air. As a pump source, the fundamental and second harmonic radiations of a femtosecond Ti:sapphire laser were used. While the fundamental laser beam had Gaussian intensity distribution and a flat phase front, the second harmonic beam had either flat or helical phase front forming an optical vortex. In both cases the angular spectra of THz radiation and azimuthal phase distributions of THz beams were investigated. It was found that when both the fundamental and second harmonic laser pulses had Gaussian profiles, the resulting THz radiation was generated as an axially symmetric cone with a flat phase front. However, when the Gaussian second harmonic beam was replaced by the one with optical singularity, the intensity and the phase of generated THz cone became modulated along the azimuthal angle. The spectrum of generated THz pulses spanned up to 50 THz in both cases. Our theoretical analysis based on the photocurrent model was in good agreement with the experimental data.
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