Orientation dependence of high-order harmonic generation in hydrogen molecular ions

We show that the direction of laser polarization with respect to the molecular axis of a linear molecule can have a significant effect on high-harmonic generation. Numerical integration of the two-dimensional Schrodinger equation of the H-2(+) and the H-3(2+) model molecular ions shows that the efficiency of some high harmonics can be higher by up to three orders of magnitude when the laser is polarized in the perpendicular direction rather than parallel to the molecular axis. We discuss experiments to test this prediction.