Spatial inhomogeneous effect on single-order harmonic enhancement

The spatial inhomogeneous effect of the laser pulse on the enhancement of the single-order harmonic has been theoretically investigated. It is shown that the single-order harmonic enhancement from the symmetric and negative inhomogeneous laser pulses presented the similar phenomena. Specifically, as the inhomogeneous parameter increases, the blue-shift of the single-order harmonic enhancement can be found. While in the case of the positive inhomogeneous effect, as the inhomogeneous parameter increases, the multiple harmonic enhancements can be found instead of the single-order harmonic enhancement. Finally, the reason behind the change of the single-order harmonic enhancement with the inhomogeneous effect is given by the time–frequency analyses of the harmonic emission process.