Five-Photon Absorption and Selective Enhancement of Multiphoton Absorption Processes

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Computational Physics

Background:

• Multiphoton absorption (MPA) is crucial for advanced optical applications.
• Understanding MPA processes, especially higher-order ones, is experimentally challenging.
• Theoretical investigations provide essential insights into MPA phenomena.

Purpose of the Study:

• To perform the first ab initio calculations of five-photon absorption.
• To investigate and compare one- to five-photon absorption in centrosymmetric molecules.
• To elucidate the underlying mechanisms governing even- and odd-photon absorption processes.

Main Methods:

• Utilizing density functional theory (DFT) for accurate electronic structure calculations.
• Calculating one-, two-, three-, four-, and five-photon absorption cross sections.
• Employing few-state models to interpret the observed absorption trends.

Main Results:

• Demonstrated distinct trends between even- and odd-photon absorption cross sections.
• Observed semiquantitative similarity in the behavior of all MPA properties.
• Showed that odd-photon absorption is dominated by one-photon strength, while even-photon absorption is dominated by two-photon strength.
• Identified the role of final excited state polarizability in modulating absorption strengths.

Conclusions:

• Odd-photon absorption is primarily governed by the one-photon absorption strength.
• Even-photon absorption is largely determined by the two-photon absorption strength.
• Developed a framework for selectively enhancing specific multiphoton absorption processes.