Figure 2

Data collapse of the fluorescence lifetime vs. depth of focus Fluorescence lifetime vs. nominal depth of focus into the solution (i.e. as shown by the microscope stand), \(z_{\hbox {F}}\), from the hydrophobic glass at \(z_{\hbox {F}}=0\). (a) Amplitude averaged lifetime as a function of \(z_{\hbox {F}}\) for various glycerol/water solutions; (b) Empirical data collapse \(R_{\tau }(z_{\hbox {F}})=(\langle \tau \rangle (z_{\hbox {F}})-\tau _{\hbox {B}})/(\langle \tau \rangle (0)-\tau _{\hbox {B}})\). Red curve: normalized distribution function \(R_{\hbox {th}}\), Eq. (10), computed by ray tracing simulation from the basic parameters of the microscope and the refractive index of the samples. Inset: Same data, showing the \(1/z_{\hbox {F}}^2\) decay of the interface contribution.