Amplitude-normalized fluorescence decay traces with excitation light parallel (red line) and perpendicular (blue line) to the apex region.
The decay trace with the diffraction-limited volume (green) provides the reference for Alexa Fluor 647 with 200 mM methyl viologen. Black lines are numerical fits used to determine the fluorescence lifetime indicated on the traces. IRF denotes the instrument response function. For a supplementary comparison between parallel and perpendicular cases, the inset displays the traces normalized so that the longer time decay component has a similar amplitude for both cases. The additional short lifetime contribution representative of the apex region clearly emerges when the polarization orientation is parallel to the apex.