Molecular Response in One-Photon Absorption via Natural Thermal Light vs Pulsed Laser Excitation

TL;DR

This paper compares molecular responses to natural thermal light and pulsed laser excitation, revealing that natural light induces incoherent responses unlike the coherent evolution caused by pulsed lasers, impacting biological process studies.

Contribution

It clarifies the fundamental differences in molecular responses to natural incoherent light versus pulsed coherent light using a quantum field approach.

Findings

Pulsed lasers induce coherent molecular evolution.

Natural thermal light results in incoherent molecular responses.

Laboratory coherence observations are not relevant to natural biological processes.

Abstract

Photoinduced biological processes occur via one photon absorption in natural light, which is weak, CW and incoherent, but are often studied in the laboratory using pulsed coherent light. Here we compare the response of a molecule to these two very different sources within a quantized radiation field picture. The latter is shown to induce coherent time evolution in the molecule, whereas the former does not. As a result, the coherent time dependence observed in the laboratory experiments will not be relevant to the natural biological process. Emphasis is placed on resolving confusions regarding this issue that are shown to arise from aspects of quantum measurement and from a lack of appreciation of the proper description of the absorbed photon.