Theoretical study of terahertz generation from atoms and aligned molecules driven by two-color laser fields

TL;DR

This paper investigates terahertz radiation generation from atoms and molecules driven by two-color laser fields using TDSE simulations, revealing key roles of ionized wave-packets, Coulomb rescattering, and molecular alignment effects.

Contribution

It provides a detailed theoretical analysis of terahertz generation mechanisms and how they depend on laser parameters and molecular alignment, advancing understanding of ultrafast electron dynamics.

Findings

Ionized wave-packet acceleration and Coulomb rescattering are crucial for THz generation.

Optimal phase delay and yield depend on laser intensity, wavelength, and duration.

THz yield correlates with molecular ionization rates and can reveal interference effects in high harmonic generation.

Abstract

We study the generation of terahertz radiation from atoms and molecules driven by an ultrashort fundamental laser and its second harmonic field by solving time-dependent Schr\"odinger equation (TDSE). The comparisons between one-, two-, and three- dimensional TDSE numerical simulations show that initial ionized wave-packet and its subsequent acceleration in the laser field and rescattering with long-range Coulomb potential play key roles. We also present the dependence of the optimum phase delay and yield of terahertz radiation on the laser intensity, wavelength, duration, and the ratio of two-color laser components. Terahertz wave generation from model hydrogen molecules are further investigated by comparing with high harmonic emission. It is found that the terahertz yield is following the alignment dependence of ionization rate, while the optimal two-color phase delays varies by a small amount when the alignment angle changes from 0 to 90 degrees, which reflects alignment dependence of attosecond electron dynamics. Finally we show that terahertz emission might be used to clarify the origin of interference in high harmonic generation from aligned molecules by coincidently measuring the angle-resolved THz yields.