Field-free orientation by a single-cycle THz pulse: The NaI and IBr molecules

Abstract

The field-free orientation induced by a single-cycle terahertz (THz) laser pulse is studied for two "heavy" molecules, NaI and IBr. Two methods are used and compared in the calculations: One is to solve the exact time-dependent Schrödinger equation (ETDSE) considering the full-rovibrational degrees of freedom, and the other is to invoke the rigid-rotor approximation (RRA). Calculations are performed for the central frequency varying from 0.05 to 1.0 THz and for the peak intensity taken to be 5 × 10(7), 2 × 10(8), and 5 × 10(8) W∕cm(2), respectively. The degree of field-free orientation, <cosθ>, is strongly dependent on the central frequency and the peak intensity of the single-cycle THz pulse. The maximum degree of field-free orientation is determined to be 0.84 for NaI and 0.63 for IBr in these given ranges of frequency and intensity. The molecular orientation obtained by the RRA calculations is in good agreement with that obtained by the ETDSE in the given parameter region.