Polarization effects in high-harmonic generation in the presence of static-electric field

We study the ellipticity dependence of the high-order harmonic generation ( HOHG) when a static electric field is presented. Through investigating the corresponding classical trajectories of the electron for the harmonic gener ation. it is found that there exists two different mechanisms. For circular ly polarized incident light the HOHG originates mainly from the recombinati on of the electrons to the nucleus after multiple returns. We also find tha t for the elliptical incidence HOHG, the application of a static electric h eld can generate harmonics far beyond the usual cutoff. [S1050-2947(99)0400 4-4].