| abstract |
A scanning confocal microscopes scans a sample (16) with an incident beam of ultraviolet radiation, in a raster scan pattern, causing the sample to fluoresce and emit visible radiation, a portion of which retraces a portion of the path optical of incident beam, to a dichroic mirror (8) that separates it from the incident beam for detection by a photomultiplier (22,26) tube. A clock signal for clocking the output of the photomultiplier tube is provided by a reference beam system that directs a reference beam (RB) onto the same scanning mirror (9) as is the incident beam, at a coincident location on that mirror, and from there through a Ronchi grating (44) having a uniform series of alternating transparent and opaque regions. The resulting pulsed reference beam is detected by a second photomultiplier tube (46), to produce a clock signal that is an accurate representation of the instantaneous scan rate of the reference beam and, thereby, the scanning incident beam. |