Long-Lasting Molecular Orientation Induced by a Single Terahertz Pulse

Area of Science:

• Molecular Physics
• Quantum Optics
• Nonlinear Dynamics

Background:

• Nonlinear polar molecules are crucial in various physical phenomena.
• Terahertz (THz) pulse excitation is a powerful tool for manipulating molecular states.
• Understanding persistent molecular orientation is key to controlling macroscopic properties.

Purpose of the Study:

• To report a novel phenomenon of persistent molecular orientation after THz excitation.
• To investigate the dependence of this phenomenon on molecular symmetry, temperature, and pulse amplitude.
• To explore potential applications of the induced macroscopic dipole moment.

Main Methods:

• Excitation of a thermal gas of nonlinear polar molecules using a single THz pulse.
• Analysis of molecular orientation dynamics using theoretical models.
• Investigation of temperature and amplitude dependencies of the residual orientation.

Main Results:

• A novel phenomenon of long-lasting molecular orientation was observed after THz pulse excitation.
• Symmetric-top molecules exhibited indefinite time-averaged orientation, while asymmetric-top molecules showed long persistence.
• Non-monotonic dependencies on temperature and amplitude were found, with optimal parameters for maximal residual orientation.

Conclusions:

• Persistent molecular orientation in nonlinear polar molecules is a significant finding.
• The induced macroscopic dipole moment offers possibilities for probing and manipulation.
• Potential applications include even harmonic generation and deflection by electrostatic fields.