Spectral redshift of high-order harmonics by adding a weak pulse in the falling part of the trapezoidal laser pulse

Pan Xue-Fei, Zhang Jun, Ben Shuai, Xu Tong-Tong, Liu Xue-Shen^†

(color online) The electric fields of the trapezoidal laser pulse (dashed red curve), the combined laser pulse (solid blue curve), and the weak laser pulse of the envelope (dotted green curve).