A device and system for measuring the multidimensional distribution of a sample tagged with a short life fluorescent label. The substance applied to a sample holder can be scanned with an optical point source excitation and read back optical stage. The sample can be excited at each of a plurality of points with a fast, e.g., nanosecond pulse of light. The resulting fluorescence can be detected after the excitation is extinguished. A detection gate window can be optimized to maximize the fluorescence signal detected for a predetermined amount of time.