Chaban Ievgeniia, Deska Radoslaw, Privault Gael, Trzop Elzbieta, Lorenc Maciej, Kooi Steven E, Nelson Keith A, Samoc Marek, Matczyszyn Katarzyna, Pezeril Thomas
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Advanced Materials Engineering and Modelling Group, Wroclaw University of Science and Technology, PL-50370 Wroclaw, Poland.
Nano Lett. 2022 Jun 8;22(11):4362-4367. doi: 10.1021/acs.nanolett.2c00771. Epub 2022 May 19.
Herein we describe a novel spinning pump-probe photoacoustic technique developed to study nonlinear absorption in thin films. As a test case, an organic polycrystalline thin film of quinacridone, a well-known pigment, with a thickness in the tens of nanometers range, is excited by a femtosecond laser pulse which generates a time-domain Brillouin scattering signal. This signal is directly related to the strain wave launched from the film into the substrate and can be used to quantitatively extract the nonlinear optical absorption properties of the film itself. Quinacridone exhibits both quadratic and cubic laser fluence dependence regimes which we show to correspond to two- and three-photon absorption processes. This technique can be broadly applied to materials that are difficult or impossible to characterize with conventional transmittance-based measurements including materials at the nanoscale, prone to laser damage, with very weak nonlinear properties, opaque, or highly scattering.
