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| 2. |
- Bergé, Luc, et al.
(author)
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THz emissions by two-color filaments in air: Revisiting the wavelength scaling
- 2019
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In: Optics InfoBase Conference Papers. - 2162-2701. ; Part F134-NLO 2019
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Conference paper (peer-reviewed)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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| 3. |
- Bergé, Luc, et al.
(author)
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Wavelength scaling of THz emissions by two-color filaments in air
- 2019
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In: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. ; June 2019
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Conference paper (peer-reviewed)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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| 4. |
- Ivanov, Maksym, et al.
(author)
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Intensity modulated terahertz vortex wave generation in air plasma by two-color femtosecond laser pulses
- 2019
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In: Optics Letters. - 0146-9592 .- 1539-4794. ; 44:15, s. 3889-3892
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Journal article (peer-reviewed)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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| 5. |
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| 6. |
- Kaltenecker, K. J., et al.
(author)
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Plasmonic Resonances Affecting Terahertz Generation in Laser-Induced Gas-Plasmas
- 2018
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In: 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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Conference paper (peer-reviewed)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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| 7. |
- Nguyen, Alisée, et al.
(author)
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Broadband terahertz radiation from two-color mid- and far-infrared laser filaments in air
- 2018
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In: Physical Review A. - 2469-9934 .- 2469-9926. ; 97:6
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Journal article (peer-reviewed)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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| 8. |
- Nguyen, Alisée, et al.
(author)
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Wavelength scaling of terahertz pulse energies delivered by two-color air plasmas
- 2019
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In: Optics Letters. - 0146-9592 .- 1539-4794. ; 44:6, s. 1488-1491
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Journal article (peer-reviewed)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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| 9. |
- Schlatter, Felix, et al.
(author)
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Project STEER : Improving the EU Tyre Noise Label
- 2022
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Conference paper (peer-reviewed)abstract
- Tyre/road noise is the dominant component of overall vehicle noise at medium and high speeds and for cars even at relatively low speeds. Consequently, road traffic noise can be reduced with the proliferation of quieter tyres. One way to achieve this is to give the tyre noise label greater attention among tyre and transportation consumers. Hence, the STEER project has evaluated the relevance and performance of the noise part of the European tyre label, looking at how it works in practice, analysing its uncertainties and suggesting how it can be improved. Its main finding is that the uncertainties in the measurement of noise level for the label are too high to be acceptable. This paper focuses on the solutions offered by STEER for an improved tyre label. With four main improvements, the overall uncertainty of the current procedure can be halved. A few possible future strategies to increase the market share of quieter tyres have been analysed and their effects quantified. If the tyre noise label is improved and the market share of quieter tyres can be increased, as project STEER proposes, area-wide reductions of up to 3 dB in road traffic noise emissions compared to the present situation are possible.
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