Ultrafast pressure-sensitive paint for shock compression spectroscopy

A pressure-sensitive paint (PSP) consisting of rhodamine 6G (R6G) dye in poly-methylacryate (PMMA) polymer is studied during nanosecond GPa shock compression created by km s^-1 laser-launched layer plates. In contrast with conventional PSP, whose response time is limited to microseconds by diffusion of O₂ in porous materials, the response time of this PSP is limited to ∼10 ns by fundamental photophysical processes. The mechanism of shock-induced PSP intensity loss is shown to be shock-enhanced intersystem crossing, which transfers some R6G population from the emissive S₁ state to the dark T₁ state. Simulations of dye photophysics and comparisons to experiment show that the PSP is sensitive to the complicated time-dependent density profiles produced in PMMA by different duration shocks. The risetime of the PSP response is limited by the S₁ lifetime under shock compression. The fall time is limited by the T₁ lifetime, which can be decreased by adding triplet quenchers. The PSP can function in two modes. When dissolved O₂ (a triplet quencher) was eliminated, the fall time became relatively slow (microseconds), and the PSP sampled the peak shock pressure and held that value for a long time. When dissolved O₂ was present, the intensity loss recovery became faster, so the PSP could function as a transient recorder of the shock-induced time-dependent density profile.