Noncontact Photoinduced Temperature Measurement via Detecting Photoacoustic Wave

Accurate measurement of photoinduced temperature rise (Δ T ) in optically absorbing thin films is important for understanding light–matter interactions, preventing laser‐induced damage, and validating photothermal models. However, existing techniques often rely on contact probes or calibration‐intensive procedures. Here we present a noncontact method for estimating Δ T using an atomic force microscopy (AFM) cantilever as a mechanical sensor of photoacoustic (PA) loading. The optical excitation is tuned to a molecular absorption resonance and intensity‐modulated at the cantilever fundamental resonance. Periodic thermoelastic expansion of the heated surface generates an acoustic pressure wave that drives the cantilever oscillation. A closed‐form relation is derived that converts the measured on‐resonance cantilever oscillation amplitude into Δ T using known cantilever, acoustic, and thermoelastic parameters. The method is demonstrated on a 500 nm poly(methyl methacrylate) (PMMA) film excited at 1733 cm −1 , where the inferred temperature rise is Δ T ≈ 1.6 K. A three‐dimensional finite‐element model coupling electromagnetic absorption and heat transfer predicts Δ T ≈ 1.4 K, in good agreement with the experiment. These results demonstrate a simple route for estimating optically induced temperature rise using standard AFM instrumentation and provide a practical tool for photothermal characterization of thin films.