THz generation from mid-infrared two-color laser pulses in air and a simple method for controlling the THz intensity

In this work, we investigated the generation of THz short pulses by two-color mid-infrared laser pulses induced gas plasma in ambient air by numerical analysis. In the simulation, the central wavelength of the input laser varied from 2.5 mu m up to 4.0 mu m. Our result indicates that the generated THz pulse intensity increases at longer wavelengths significantly. In our simulations, the fundamental pulse intensity and duration were kept fixed yielding no significant difference between the generated electron densities indicating that the asymmetry of the electric field has a major role in the THz generation efficiency by increasing the velocity of electrons. Our results also show that the fundamental pulse and the THz pulse can spectrally overlap, which makes it difficult to separate them spectrally. The possibility of the relative phase control between the fundamental and the second harmonic pulses with a single plate is also examined. Our calculations show that the best materials are the fluorides for controlling the relative phase.