Ab Initio Cluster Approach for High Harmonic Generation in Liquids

Area of Science:

• Quantum Optics and Laser Physics
• Computational Chemistry and Materials Science
• Condensed Matter Physics

Background:

• High harmonic generation (HHG) is well-understood in gases and solids, but a theoretical framework for liquids is lacking.
• Existing models for gases and solids are not directly applicable to the unique environment of liquids.
• This gap hinders the study of nonlinear optical phenomena and ultrafast dynamics in liquid systems.

Purpose of the Study:

• To develop a robust and accurate ab initio computational approach for simulating high harmonic generation (HHG) in bulk liquids.
• To investigate the nonlinear optical response of different liquid types, including polar and nonpolar substances.
• To identify unique spectral signatures of HHG in liquids that can be exploited for advanced characterization techniques.

Main Methods:

• Development of a cluster-based, ab initio approach grounded in time-dependent density functional theory (TDDFT).
• Incorporation of approximations to ensure computational feasibility and accuracy for realistic liquid systems.
• Application of the method to perform HHG calculations for water, ammonia, and methane liquids.

Main Results:

• Successful demonstration of the computational approach for simulating HHG in various liquids.
• Comparison of distinct HHG spectral characteristics between polar (water, ammonia) and nonpolar (methane) liquids.
• Identification of a novel spectral minimum (15-17 eV) in liquid methane, exclusive to the liquid phase, linked to its structure.

Conclusions:

• The developed ab initio cluster-based method provides a powerful tool for calculating HHG in liquids.
• The findings highlight the unique nonlinear optical properties and dynamics inherent to liquid systems.
• The identified spectral features in liquid methane offer potential for novel ultrafast spectroscopy applications.