In this publication, the generation of terahertz pulses from two-color mid-infrared pulses is investigated in ambient air by numerical simulations. In these simulations, the central wavelength of the fundamental laser pulse is varied from 1.6 µm up to 10 µm. As expected, the results show that the ionization efficiency decreases at longer wavelengths, while the electron acceleration efficiency increases, resulting the highest THz pulse generation around 8.2-8.5 µm. At the 8.2-8.5 µm the generated THz electric field peak intensity is hundred times more compared to the Ti:Sapphire lasers, which are the most commonly used lasers for this type of THz generation. We show that optimal phase control between the second harmonics and the fundamental pulse can be achieved with the help of thin plates of barium, calcium and lithium fluorides.
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