Bleaching and stimulated recovery of dyes and of photo-cantilevers

TL;DR

This paper investigates how intense light causes deep penetration and non-linear bleaching in absorbing media, affecting the bending of dye-loaded nematic photo-solids, with a focus on stimulated recovery and thermal effects.

Contribution

It introduces a detailed analysis of non-linear absorption and stimulated recovery in dye media, applying it to the mechanical bending of photo-responsive nematic cantilevers.

Findings

Stimulated recovery significantly affects dye bleaching dynamics.

Optically-generated heat has minor impact compared to optical effects.

Non-linear absorption enables bending beyond Beer's Law predictions.

Abstract

We examine how intense optical beams can penetrate deeply into highly absorbing media by a non-linear, photo-bleaching process. The role of stimulated recovery to the dye ground state can be important and is delineated. This analysis of non-linear absorption processes is applicable in general to situations where chromophores are irradiated, for instance in biology. We examine the implications for the bending of cantilevers made of heavily dye-loaded nematic photo-solids, that is nematic glasses and elastomers that have large mechanical reactions to light. In particular we describe the bending of cantilevers sufficiently absorbing that they would not bend if Beer's Law were applicable. We quantify the role of optically-generated heat in determining the mechanical response and conclude that in general it is minor in importance compared with optical effects.