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PRESSURE-SENSITIVE paint (PSP) is an optical pressure sensor that utilizes the oxygen quenching of luminescence. PSP measurements in unsteady aerodynamic ows require fast time response of the paint. 1¡ 3 There are two characteristic timescales that are related to the time response of PSP. One is the luminescent lifetime representing an intrinsic physical limit for the achievable temporal resolution of PSP. Another is the timescale of oxygen diffusion across the PSP layer. When the timescale of oxygen diffusion is much larger than the luminescent lifetime, the time response of PSP is controlled by oxygen diffusion. In a thin homogeneouspolymer layer where diffusion is Fickian, the oxygen concentration [O2] can be described by the diffusion equation in one dimension: