We develop the model of the acoustic wave emission by the femtosecond filament and the model of optical nanosecond pulse guiding in the transient waveguide created as a result of interference of acoustic waves diverging from the filaments array. The numerical algorithms and appropriate solvers are created. In the simulation we identify two regions of time delays between the femtosecond pulse launching the acoustic waves and the nanosecond guided pulse, where the optical guiding is achieved with the high and moderate quality.
Spatio-spectral distribution of THz radiation generated by two-color femtosecond laser breakdown in air is investigated theoretically. The theoretical model is based on the fast oscillating light field propagation and self-consistent free electron generation process. We find that the THz emission spectrum has both the low-frequency component related to the transient photocurrent with the maximum spectral intensity at ~1 THz, and the high-frequency component at ~10 THz related to the nonlinear response of bound electrons.