Abstract-Intensity modulated terahertz vortex wave generation in air plasma by two-color femtosecond laser pulses

Maksym Ivanov, Illia Thiele, Luc Bergé, Stefan Skupin, Danas Buožius, Virgilijus Vaičaitis,

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-15-3889

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.

© 2019 Optical Society of America

Abstract-Terahertz vortex wave generation in air plasma by two-color femtosecond laser pulses

Maksym Ivanov, Illia Thiele, Luc Bergé, Stefan Skupin, Danas Buožius, Virgilijus Vaičaitis

https://arxiv.org/abs/1906.06243

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 such 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 produces 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.

Abstract-Towards broadband terahertz generation due to coherent phonon–polariton excitations in centrosymmetric media

Eugenijus Gaižauskas, Virgilijus Vaičaitis, Olga Fedotova, and Oleg Khasanov  »View Author Affiliations

http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-5-3-623

Optical Materials Express, Vol. 5, Issue 3, pp. 623-628 (2015)
http://dx.doi.org/10.1364/OME.5.000623

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In this work, four-wave difference-frequency generation in centrosymmetric media doped with three-level quantum systems is investigated theoretically. Terahertz radiation generation in the coherent regime of interaction, where the durations of optical pulses are shorter than the relaxation time of coherences induced in two- and one-photon resonant transitions, is analyzed. It is shown that the coherent regime of four-wave frequency mixing enhances the efficiency of radiation generation in the terahertz frequency range. Quantum confined systems (e.g., atoms and molecules in nanoparticles) should be considered as possible media for practical implementation of the method.

© 2015 Optical Society of America