Characterization of frequency response of pressure-sensitive paints

Systematic experiments have been carried out for two different types of fast-responding pressure-sensitive paint (PSP): one is polymer/ceramic (PC) PSP, and the other is anodized-aluminum (AA)-PSP. The frequency characteristics of these paints were measured, and their transfer functions were calculated from those data. Two luminophores having different luminescent lifetimes were applied on those PSP samples. The thickness and temperature of the binder were also changed to separate the effects of the photochemical reaction time from those of the oxygen diffusion time. The PSP sample plate was excited by a UV laser with 400 nm wavelength. The emission light of PSP was collected by two lenses and measured by a photomultiplier tube (PMT) with an optical filter suitable for the emission wavelength of the luminophore painted on the sample plate. It was shown that the dominant factor of the frequency characteristics of PC-PSP is the luminescent lifetime and the transfer function of PCPSP is approximated by the first-order system. On the other hand, the frequency characteristics of AA-PSP are more complicated since the system depends on both the luminescent lifetime and the diffusivity of oxygen into the binder. The transfer functions of AA-PSPs with RuDPP and TCPP are approximated by the first-order and ½-order systems, respectively. These differences should be attributed to the difference in the luminescent lifetime of those two luminophores. The results of this study suggest that luminophore molecules are distributed near the surface of PC-PSP and on the other hand are adsorbed inside the pores of AA-PSP.