Multi-directions pure even harmonic simultaneous generation from planar molecules in linearly polarized laser fields

Abstract

Previous studies have found that pure even harmonics are generated from oriented CO molecules in linearly polarized laser fields. In this work, we demonstrate multi-directions pure even harmonic simultaneous generation from planar molecules in linearly polarized laser fields using the time-dependent density-functional theory. The analysis reveals that pure even harmonic generation depends on the special symmetry of the planar molecule. In the linearly polarized laser field, it is found that only when the planar molecules have reflective symmetry direction and the molecules perpendicular to the reflective symmetry direction do not have reflection symmetry can the planar molecules generate pure even harmonics along such reflective symmetry direction. When the laser polarization is perpendicular to the planar molecule, if the molecule has several these directions of such reflection symmetry, pure even harmonics will be simultaneously generated along these symmetrical directions. Moreover, when the laser polarization is along the molecular plane and perpendicular to the direction of one such reflection symmetry, even harmonic is also generated along this reflection symmetry direction, whereas odd harmonic is generated along the direction of laser polarization. The phenomenon exists in all polyatomic planar molecules with such reflection symmetry.