Non-linear dynamics of absorption and photo-bleaching of dyes

TL;DR

This paper investigates the non-linear dynamics of dye absorption and photo-bleaching, focusing on azobenzene isomerization, revealing that non-linear effects are common and weakly dependent on dye concentration and viscosity.

Contribution

It experimentally characterizes non-linear absorption regimes in dyes, especially azobenzene, and identifies key transition rate constants relevant for practical applications.

Findings

Non-linear absorption is prevalent in thick samples.

Crossover to non-linear regime weakly depends on dye concentration.

Transition rate constants are experimentally determined.

Abstract

The celebrated Lambert-Beer law of light absorption in photochromic media is only valid at low intensities of incident light and low concentration of chromophore. Here we address the generic problem of photo-absorption dynamics, experimentally studying the case of azobenzene isomerization. We show that the non-linear regime is very common and easy to achieve in many practical situations, especially in thick samples where the light depletes the chromophore in the first layers and can propagate through the medium with a sub-exponential law. Importantly, the crossover into the non-linear absorption regime only weakly depends on the dye concentration and solution viscosity. We experimentally quantify the characteristics of this peculiar optical response and determine the key transition rate constants.