Quantum dynamics of a polar rotor acted upon by an electric rectangular pulse of variable duration

TL;DR

This paper investigates how rectangular electric pulses of variable duration influence the quantum dynamics of a polar rotor, revealing quasi-periodic energy drops due to oscillating wavepacket populations, supported by analytical and numerical analysis.

Contribution

It demonstrates that rectangular pulses can replicate previously observed energy drops in quantum rotors and provides analytic formulas to predict these effects.

Findings

Energy drops occur at specific pulse durations.

Oscillating wavepacket populations cause the energy drops.

Analytic formulas predict diminished energy transfer and orientation.

Abstract

As demonstrated in our previous work [J. Chem. Phys. 149, 174109 (2018)], the kinetic energy imparted to a quantum rotor by a non-resonant electromagnetic pulse with a Gaussian temporal profile exhibits quasi-periodic drops as a function of the pulse duration. Herein, we show that this behaviour can be reproduced with a simple waveform, namely a rectangular electric pulse of variable duration, and examine, both numerically and analytically, its causes. Our analysis reveals that the drops result from the oscillating populations that make up the wavepacket created by the pulse and that they are necessarily accompanied by drops in the orientation and by a restoration of the pre-pulse alignment of the rotor. Handy analytic formulae are derived that allow to predict the pulse durations leading to diminished kinetic energy transfer and orientation. Experimental scenarios are discussed where the phenomenon could be utilized or be detrimental.