Figure 2. Volume element in confocal system. Through a dichroic mirror, laser light of a point source excites fluorescent molecules within sample droplet or cell if they are within volume element. Fluorescence from volume element alone is detected by photodiodes behind pinhole

From

Fluorescence Correlation Analysis for Diagnosis Based on Molecular Dynamics

Yasutomo Nomura

Biomedical Science and Engineering. 2016, 4(1), 23-30 doi:10.12691/bse-4-1-3