Modulation of terahertz-spectrum generation from an air plasma by tunable three-color laser pulses

We theoretically demonstrate that the terahertz-spectrum generation in three-color laser-gas interactions can be effectively manipulated by tuning the laser wavelengths. We show that by positive and negative detuning of one of the color laser wavelengths in the three-color laser pulse, the terahertz spectral range can be greatly expanded, and in particular, the high spectral frequency components emerge. However, the total terahertz energy is maintained at a relatively high level and can even significantly increase. Moreover, we also show that the middle and high spectral frequency components of the terahertz spectrum can be effectively tuned by modulating the relative wavelength of the three-color laser pulses. Finally, our analysis shows that the ionization events play an important role in the intense and shaped terahertz generation.