Rolled-up nanomembrane microtube cavities support tailored higher-order whispering-gallery-mode resonances, enabling spatially resolved detection of laser irradiation-induced water molecule desorption from hydrophobic oxide surfaces. In particular, the ultra-thin cavity wall significantly enhances surface sensitivity via intense evanescent fields, allowing real-time monitoring of sub-monolayer desorption events through resonance wavelength blueshifts. By leveraging distinct responses from various axial modes, ranging from the fundamental mode up to the fourth order mode, the system locally probes photothermal desorption dynamics initiated by a tightly focused laser beam. The experimental data are quantitatively analyzed using a combined kinetic model, which reveals an initial rapid desorption phase followed by a slower equilibration process. This methodology provides new insights into molecular desorption kinetics and establishes a robust platform for investigating surface molecular dynamics.
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