Mechanism of Molecular Orientation by Single-cycle Pulses

TL;DR

This paper demonstrates that single-cycle THz pulses can induce significant and persistent molecular orientation through quantum interference effects, even with symmetric pulses and zero-area conditions.

Contribution

It reveals a novel mechanism where quantum interference among eigenstates enables net molecular orientation using symmetric, zero-area pulses over a rotational period.

Findings

Large peak instantaneous orientations achieved.

Nonzero time-average orientations over a rotational period.

Orientation mechanism works regardless of rotational constant.

Abstract

Significant molecular orientation can be achieved by time-symmetric single-cycle pulses of zero area, in the THz region. We show that in spite of the existence of a combined time-space symmetry operation, not only large peak instantaneous orientations but also nonzero time-average orientations over a rotational period can be obtained. We show that this unexpected phenomenon is due to interferences among eigenstates of the time-evolution operator, as was described previously for transport phenomena in quantum ratchets. This mechanism also works for sequences of identical pulses, spanning a rotational period. This fact can be used to obtain a net average molecular orientation regardless of the magnitude of the rotational constant.