Optically probing picometer-resolved photo-dynamics of solid surfaces

Optical probes for precisely studying laser-solid interactions are of utmost importance in various fields. Here we demonstrate a simple, single-lens interferometer for measuring time-resolved deformation of solid surfaces induced by optical excitation with about 150 pm (λ/4000) precision by analyzing the local intensity of the interference fringes in a self-referencing manner. We first show picometer-resolved deformation and relaxation of a smooth acrylic surface due to absorption of a sub-mW low-power laser pulse. We demonstrate the applicability of our approach to samples producing non-specular reflections, such as a dried drop of blood and a black rough surface of graphene oxide, prepared by drop-casting on a glass slide. We suggest that the thermo-mechanical deformation from our interferometer can be used to measure thermal effects (such as the local change in temperature) of different solid materials with high precision, which is needed in many applications such as in laser heating or cooling experiments. It will be interesting to extend our approach to study real-time thermal and non-thermal deformation in solids due to nanosecond or picosecond laser pulses.