Influence of Kerr nonlinearities on THz radiation generation in air by bichromatic femtosecond laser pulses

The dependence of terahertz (THz) radiation generation in air by femtosecond laser pulses on frequency and the relative phase between two-color pump waves was analyzed experimentally and numerically. It was found that although the laser-induced plasma microcurrents remains the main mechanism of THz radiation generation within the whole spectral range, the four-wave mixing modifies the generation process. This modification makes maximal generation efficiency dependent not only on the relative phase between the pump waves but also on the frequency of the emitted radiation. This should be taken into account during the optimization of the generation process in specific spectral ranges.