Temperature amplification during laser heating of polycrystalline silicon microcantilevers due to temperature-dependent optical properties

The absorption of optical energy and subsequent thermal transport are investigated experimentally and numerically for 500 μm long, 250 μm wide, and 2.25 μm thick polycrystalline silicon microcantilevers irradiated by an 808 nm continuous-wave laser. Temperature profiles were measured using Raman thermometry at 314 and 532 mW of laser power, and the microcantilever peak temperature was measured for laser powers up to 719 mW. A modular technique for multilayered structures is used to calculate the optical absorption in polysilicon microcantilevers, and the thermal response is then calculated with a two-dimensional, finite difference model. Very good agreement is obtained between the measured and calculated temperature profiles and peak temperatures versus laser power. The abrupt increase or amplification of peak temperature for laser powers between 415 and 440 mW is shown to be a result of peaks in the temperature-dependent optical absorptance.