Abstract-Terahertz pulse generation by two-color laser fields with circular polarization

C. Tailliez, A. Stathopulos, S. Skupin, D. Buožius, I. Babushkin, V. Vaičaitis, L. Bergé

https://arxiv.org/abs/2007.08191

We study the influence of the polarization states of femtosecond two-color pulses ionizing gases on the emitted terahertz radiation. A local-current model and plane-wave evaluations justify the previously-reported impact on the THz energy yield and an (almost) linearly-polarized THz field when using circularly-polarized laser harmonics. For such pump pulses, the THz yield is independent on the relative phase between the two colors. When the pump pulses have same helicity, the increase in the THz yield is associated to longer ionization sequences and higher electron transverse momenta acquired in the driving field. Reversely, for two color pulses with opposite helicity, the dramatic loss of THz power comes from destructive interferences driven by the highly symmetric response of the photocurrents lined up on the third harmonic of the fundamental pulse. While our experiments confirm an increased THz yield for circularly polarized pumps of same helicity, surprisingly, the emitted THz radiation is not linearly-polarized. This effect is explained by means of comprehensive 3D numerical simulations highlighting the role of the spatial alignment and non-collinear propagation of the two colors.

Abstract-Generation of Terahertz Radiation by Two-Color Ionizing Laser Pulses with Arbitrary Intensity Ratios

Ivan Laryushin

https://www.mdpi.com/2304-6732/7/2/38

The dependence of the terahertz energy generated by two-color femtosecond ionizing pulses on intensities of both one-color components is studied. The numerical calculations are supported with analytical formulas which help to reveal the nature of these dependences. The optimal intensity ratios in the cases when the frequency ratios in two-color pulse are equal to 2, 3/2 and 4 are found.

Abstract-Contribution of the optical rectification in terahertz radiation driven by two-color laser induced plasma

Hang Li, Ying Zhang, Wenfeng Sun, Xinke Wang, Shengfei Feng, Peng han, Jiasheng Ye, and Yan Zhang

Schematic diagram of the experimental setup.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-4-4810

In the terahertz (THz) generation driven by two-color laser pulses, the THz wave radiated from the BBO crystal as the effect of the optical rectification is always assumed to be less and negligible. In this paper, the contribution of the optical rectification in the THz radiation driven by two-color laser pulses has been determined quantitatively, by the crucial factors including BBO crystal rotation angle, the pump power of laser, and the numerical aperture of lens. The experimental and simulation results show that the above related factors have dramatically affected the intensity ratio of the THz waves from the plasma and BBO crystal. It is helpful for understanding the mechanism of THz generation from air plasma.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Controlling Amplitude and Radiation Pattern of Emitted Terahertz by Group Velocity Mismatch

 H. Sobhani, H. Zakeri-Khatir, A. Shekari Firouzjaei,

https://ieeexplore.ieee.org/document/8408828/

In this paper, effect of group velocity mismatch on the characteristic of terahertz radiation from a plasma irradiated by two color laser pulses is investigated. The group velocity mismatch is directly related to the slippage-limited interaction length. In order to control the characteristic of generated terahertz radiation, the slippage-limited interaction length effect on radiation pattern and electric field amplitude is investigated. The slippage-limited interaction length can be controlled by the background plasma density. By rising the plasma density, the slippage-limited interaction length is decreased. Consequently, the terahertz electric field amplitude is reduced and the radiation pattern is modified. In addition, by tuning the plasma density, the power pattern directivity and the side lobe level are controlled.