Controlling circularly polarized high-order harmonic generation in molecules by intense tricircular laser pulses

Abstract

We present a scheme to control circularly polarized high-order harmonic generation (HHG) in molecules, the source of extreme ultraviolet and x-ray pulses, by multiple frequency co- and counter-rotating circularly polarized laser pulses. Simulations are performed on the oriented single electron molecular ions with cyclic equilateral geometry, ${\mathrm{H}}_{3}^{2+}\phantom{\rule{4.pt}{0ex}}\text{and}\phantom{\rule{4.pt}{0ex}}{\mathrm{H}}_{4}^{3+}$, as benchmark models, by numerically solving time-dependent Schr\"odinger equations. Results show that circularly polarized HHG can be produced with extended harmonic order cutoffs, which depend on the intensity ratio of fields and the field-molecule symmetry. We describe the laser induced electron dynamics in a rotating frame to examine recollision dynamics and Coriolis effects. The resulting modulation of HHG spectra arises from a combination of two bicircular fields with counter-rotating and co-rotating components. It is also found that harmonic polarization is a function of the pulse frequencies and helicities, illustrating the importance of matching the field-molecule symmetry. The results in principle illustrate a method for controlling circular polarization properties of harmonics in molecules.