Molecular Level-Crossing and the Geometric Phase Effect from the Optical Hanle Perspective

TL;DR

This paper investigates how the geometric phase and wave packet momentum influence the lifetime and coherence in molecular level-crossing, using chirped pulses to control and measure these effects through fluorescence interference.

Contribution

It introduces the concept of wave packet momentum lifetime and demonstrates control of molecular coherence via chirped pulses affecting geometric phase interference.

Findings

Chirped pulses modulate wave packet coherence and lifetime.

Geometric phase influences interference pathways in excited states.

Wave packet momentum lifetime depends on chirp rate.

Abstract

Level-crossing spectroscopy involves lifting the degeneracy of an excited state and using the interference of two nearly degenerate levels to measure the excited state lifetime. Here we use the idea of interference between different pathways to study the momentum-dependent wave packet lifetime due an excited state level-crossing (conical intersection) in a molecule. Changes in population from the wave packet propagation are reflected in the detected fluorescence. We use a chirped pulse to control the wave packet momentum. Changing the chirp rate affects the transition to the lower state through the conical intersection. It also affects the interference of different pathways in the upper electronic state, due to the geometric phase acquired. Increasing the chirp rate decreases the coherence of the wave packet in the upper electronic state. This suggests that there is a finite momentum dependent lifetime of the wave packet through the level-crossing as function of chirp. We dub this lifetime the wave packet momentum lifetime.