Figure 3. Schematics and operating principle of multiphase interferometric microscope illustrating how z-position is resolved.

( a, b) Schematic of the single-photon multiphase fluorescence interferometer. A point source with z-position δ emits a single photon both upwards and downwards. These two beams (color-coded as red and green in ( b) interfere in a special three-way beam splitter. ( c) The self-interfered photon propagates to the three color-coded charge-coupled device (CCD) cameras with amplitudes that oscillate 120° out of phase as indicated. a.u., arbitrary units; BP, band pass; NA, numerical aperture. Taken from 49.