Phase relations between focused bichromatic laser pulses in terahertz wave generation from gas plasma

►Terahertz emission from air excited by focused bichromatic laser pulses was investigated. ►Curved phase fronts of the pump cancel each other resulting in a flat front at terahertz frequency. ►In contrast to the plane-wave approximation the yet unreported phase term has been found. ►A good agreement between the theoretical and experimental data has been obtained.