A typical laser-scanning confocal microscope. The instrument consists of a conventional fluorescence microscope (enclosed in the lower shaded rectangle) to which has been attached a confocal-scanning unit (upper shaded rectangle) comprising a pair of scanning mirrors, a laser, some wavelength-selective filters, a pinhole aperture, and a photomultiplier detector. The laser illumination is directed down the phototube of the microscope, having been deflected by the rapidly oscillating scanning mirrors so that it sweeps across the specimen in a raster pattern. Fluorescent light emitted by the sample passes back up through the phototube, is descanned by the scanning mirrors, and passes through the dichromatic beam splitter (which removes any reflected laser light) to the pinhole aperture. Light originating from the focal plane passes through the pinhole to the detector, but all other light is blocked. For reflectance imaging, the dichromatic beam splitter is replaced by a half-silvered mirror. A sliding prism allows visual (nonconfocal) observation through the usual binocular eyepieces, using the normal microscope lamps for illumination.