Accurate modeling and characterization of photothermal forces in optomechanics

Photothermal effects have been pointed out as prominent sources of forces in optomechanical systems, competing with the standard radiation pressure interactions. In this Letter, we derive a novel and accurate model for the prediction of photothermal forces. Based on thermodynamic considerations, we properly account for strong photothermal surface effects. As a proof-of-concept, we perform numerical and experimental tests on GaAs microdisks cavities and obtain striking agreement with our theoretical framework, revealing the importance of surface photothermal forces in microphotonic devices.