Logarithmic confocal distance measurement

This research presents a method and results based on confocal microscopy for noncontact axial distance measurement from a lens to a partially reflective surface using an array of

photodetectors. The ratio of the photodetector signals is independent of the surface reflectivity and light source variations over a range of distance. By using logarithmic photodetector signals the object distance is proportional to the difference between the signals. This technique potentially allows measurement of sound produced by single living cells, or the high velocity surface shape changes in the hohlraum in laser fusion experiments.