THz generation by dual-color pulse in prealigned molecules

TL;DR

This paper demonstrates how field-free molecular alignment can coherently control terahertz (THz) generation in air using dual-color pulses, enabling modulation of THz intensity and polarization through molecular alignment and plasma effects.

Contribution

It introduces a novel method to control THz generation via molecular alignment, including polarization control and plasma effects, in air with dual-color pulses.

Findings

THz generation can be enhanced or suppressed by molecular alignment timing.

Polarization of THz radiation can be controlled using molecular alignment as a transient wave-plate.

Plasma effects influence the intensity and polarization of the generated THz radiation.

Abstract

We demonstrate that the THz generation in air from a dual-color pulse, composed of the fundamental and second-harmonic waves, can be coherently controlled by field-free molecular alignment. By tuning its time delay to properly match various molecular alignment revivals, the THz generation from the dual-color pulse can be promoted or decreased due to the spatial cross-(de)focusing effect and the alignment-dependent ionization probabilities of the prealigned diatomic molecules of air. For the dual-color pulse of orthogonally polarized fundamental and second-harmonic waves, the polarization of the generated THz radiation can be controlled by the field-free molecular alignment, which functions as a transient dynamic wave-plate for the dual-color pulse with different phase velocities for the orthogonally polarized field components. The plasma effect on the THz generation of the dual-color pulse is also observed, leading to additional intensity and polarization control of the THz radiation.