Determination of linear and nonlinear absorption of metallic colloids using photothermal lens spectrometry

We report on pump-probe mode-mismatched photothermal lens experiments of metallic micro- and nanoparticle water solutions. We show that metallic colloids exhibit nonlinear absorption effects related to the forces that result from the interaction with the electromagnetic radiation. The colloids show a double peak Z-scan shape that is associated with the presence of attraction forces when irradiating at 400 nm. We estimate the corresponding nonlinear absorption coefficients using a Fresnel diffraction approximation for the description of the signal.