Probing orientation degrees of polar molecule from high-order harmonic generation: the case of partial alignment

Abstract

Recently, we have proposed a general method to probe the whole range of degrees of orientation based on the time-frequency profile of high-order harmonic generation (HHG) but for perfectly aligned polar molecules only. In this study, we expand the previous results by considering the imperfect alignment of an ensemble of polar molecules. The “experimental” HHGs with molecular alignment distribution are simulated by numerically solving the time-dependent Schrödinger equation. The results show that, for high and moderate degrees of alignment, the proposed method is still effective and robust. For an ensemble with low degrees of alignment, the systematic error is significant due to the inaccuracy caused by the molecules aligned at large angles to the laser electric field.