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13THz-O-2
Properties of backward terahertz emission from two-color laser induced microplasma
A. Ushakov1, P. Chizhov1, N. Panov2, S. Daniil2, V. Bukin1, A. Savel'ev2, O. Kosareva2, S. Garnov1
1Prokhorov General Physics Institute of the Russian Academy of Sciences, Oscillation, Moscow, Russian Federation
2Lomonosov Moscow State University, Physics, Moscow, Russian Federation
Femtosecond laser induced plasma in gas media is one of the key sources of terahertz (THz) radiation for different applications [1]. To reach a high power THz pulses in these sources two-color femtosecond pulses (basically consist of fundamental wave and its second harmonic) are typically used [2]. One of the main research directions for these sources is investigation of output angular distribution of THz emission in terms of focusing regime of two-color pump pulses [3]. A special interest is connected with tight focusing regime, which leads to forming of a subwavelength plasma channel (so-called "microplasma") [4]. For these sources output angular distribution of THz emission is broad, and there is some part of THz emission that can spread from induced by two-color pulses microplasma in opposite direction to propagation of two-color pump (so-called "backward" THz emission) , that has been demonstrated experimentally [5].
In this work we study experimentally the properties of "backward" THz emission from microplasma induced by two-color femtosecond laser pulses: waveform, spectrum and energy. By the controlled reflection of the propagated in forward direction THz emission, we observe "backward" and "forward" THz emissions in the same waveform and thus evidenced of the existence of "backward" THz emission. The comparative spectral analysis of "backward" and "forward" THz emission is demonstrated. A shift of maximum in low-frequency region for "backward" THz emission in comparison with "forward" one is observed. Measurements of the energy of "backward" and "forward" THz emissions provide its ratio to be ~5.5% in terms of two-color pump energies in region 1.2-2 mJ. All of these results are in good agreement with numerical simulations in the framework of interferometric model [6].
References
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