Abstract-Comparison of terahertz radiation spectra emitted from single-color IR and UV filaments

G. E. Rizaev, Ya. V. Grudtsyn,  A. A. Ionin,  O. G. Kosareva, A. V. Koribut;, Yu. A. Mityagin,  D. V. Mokrousova,  N. A. Panov,  S. A. Savinov,  L. V. Seleznev,  D. E. Shipilo,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11322/113222D/Comparison-of-terahertz-radiation-spectra-emitted-from-single-color-IR/10.1117/12.2543372.short

Emission of THz radiation from a single-color ultraviolet (248 nm) and infrared (744 nm) filament in air is studied experimentally and compared at similar pulse durations, focusing conditions and excess of peak pulse power over the critical power for self-focusing. An angular distribution of the terahertz emission for both ultraviolet and infrared pump is conical with the closed cone angle. In contrast, the terahertz radiation energy and spectrum differ significantly. The energy of terahertz emission from ultraviolet filament is 1-2 orders of magnitude lower than the terahertz yield from the infrared filament. The terahertz spectrum of ultraviolet filament is shifted to the low-frequency range and narrower as compared to the spectrum of terahertz emission from infrared filament. We explain qualitatively the difference in terahertz yields and spectra by lower intensity and plasma density in the ultraviolet filament. Similar behavior of THz spectra is observed when changing the IR filament parameters.

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Abstract-Waveform, spectrum, and energy of backward terahertz emission from two-color femtosecond laser induced microplasma

Applied Physics Letters

 A. A. Ushakov,   N. A. Panov,   P. A. Chizhov,  D. E. Shipilo,  V. V. Bukin, A. B. Savel'ev, S. V. Garnov, O. G. Kosareva,

https://aip.scitation.org/doi/abs/10.1063/1.5080338

We measured the key characteristics of the backward terahertz (THz) emission from a two-color femtosecond laser spark in air: waveform, spectrum, and energy. Through the controlled reflection of the forward THz pulse, we observed the backward and forward ones in the same waveform and hence directly evidenced the origin of the backward THz radiation from the plasma spark. The spectrum of the backward THz radiation is shifted to the low-frequency range as compared with the forward one. Measurements of the energy of the backward and forward THz pulses for different pump pulse energies provide their ratio to be ∼5.5%, which quantitatively agrees with the results of our numerical simulations. These results can be useful for the noninvasive monitoring of forward THz emission parameters by the backward one.

Abstract-Backward terahertz radiation from the two-color femtosecond laser filament

A. A. Ushakov, M. Matoba, N. Nemoto, N. Kanda, K. Konishi, P. A. Chizhov, N. A. Panov, D. E. Shipilo, V. V. Bukin, M. Kuwata-Gonokami, J. Yumoto, O. G. Kosareva, S. V. Garnov, A. B. Savel’ev


https://link.springer.com/article/10.1134%2FS0021364017230047

We report the first experimental observation of backward terahertz emission from the two-color laser induced plasma filament in air. The ratio of measured forward-to-backward terahertz radiation is ∼25/1. This result agrees with numerical simulations based on interferometric model assuming 0.3 mm long plasma source.

Abstract-Ultrabroad terahertz spectrum generation from an air-based filament plasma

V. A. Andreeva, O. G. Kosareva, N. A. Panov, D. E. Shipilo, P. M. Solyankin, M. N. Esaulkov, P. González de Alaiza Martinez, A. P. Shkurinov, V. A. Makarov, L. Bergé, and S. L. Chin

https://journals.aps.org/prl/accepted/4507aYb8Wf411d4d98f601634b2a9b1dd8b3ddd05

We have solved the long standing problem of the mechanism of terahertz (THz) generation by a two-color filament in air and found that both neutrals and plasma contribute to the radiation. We reveal that contribution from neutrals by four-wave mixing is much weaker and higher in frequency than the distinctive plasma lower frequency contribution. The former is in the forward direction while the latter is in a cone and reveals an abrupt downshift towards near the plasma frequency. Ringshaped spatial distributions of the THz radiation are shown to be of universal nature and they occur in both collimated and focusing propagation geometries. Experimental measurements of the frequency-angular spectrum generated by 130-fs laser pulses agree with numerical simulations based on a unidirectional pulse propagation model.

Abstract-Transformation of terahertz spectra emitted from dual-frequency femtosecond pulse interaction in gases

                   

                                                      

A. V. Borodin, N. A. Panov, O. G. Kosareva, V. A. Andreeva, M. N. Esaulkov, V. A. Makarov, A. P. Shkurinov, S. L. Chin, and X.-C. Zhang  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-38-11-1906

We demonstrate that the two basic physical mechanisms of terahertz (THz) generation in a femtosecond filament, namely, the free electron photocurrent and the nonlinear polarization of neutrals, can be identified through the spectral analysis of THz radiation. The contribution from the photocurrent peaks at the units of THz, while the neutrals yield the peak at the tens of THz. We suggest the practical implementation of such spectral analysis by varying the initial transform-limited laser pulse duration.

© 2013 Optical Society of America