Spatiotemporal 4D photoacoustic temperature reconstruction of laser-induced photothermal heating on plasmonic surfaces

• Photoacoustic imaging enables label-free 4D temperature mapping • Surface and volumetric thermal fields are resolved simultaneously • High-resolution thermoplasmonic dynamics are visualized in real time • The method is validated by experiments and theoretical modeling • Feasibility is demonstrated in microfluidic flow environments We report a spatiotemporal four-dimensional (4D) photoacoustic (PA) thermometry approach for quantitative temperature reconstruction of laser-induced photothermal fields on plasmonic surfaces. Using titanium nitride (TiN) nanofilms as thermoplasmonic absorbers, two complementary PA observables, amplitude and time shift, are jointly analyzed to reconstruct temperature distributions with micrometer-scale spatial resolution and millisecond-scale temporal resolution. This capability is achieved through single-point measurements combined with model-based reconstruction using PA microscopy. The PA amplitude reveals the two-dimensional surface temperature field, while the time-shift analysis enables model-based reconstruction of the third-dimensional thermal profile extending into the surrounding medium. A theoretical heat transfer model is validated by the experimental results, demonstrating excellent agreement. The proposed technique further visualizes real-time heat diffusion dynamics, establishing a framework for 4D thermometry. Moreover, the approach proves feasible for visualizing thermal fields under microfluidic flow. This label-free method offers new physical insights into energy conversion and heat transport, and paves the way for advanced studies in thermoplasmonics, microfluidics, and thermal management at the microscale.