resolution is required, two-photon microscopy is often coupled with confocal
detection (by a pinhole) [8], or two-beam interference illumination is combined
with confocal detection [9].
14.2.4 Other Three-Dimensional
Microscopy Techniques
Recent years have seen the development of several other methods for
three-dimensional microscopy. Optical coherence tomography (OCT) is a 3-D
microscopy technique in which axial resolution is improved by interferometric
measurement of the time-of-flight of short-coherence light [10]. Typically,
a Michelson-type interferometer is illuminated by a femtosecond laser pulse or
superluminescent light-emitting diode (LED) light, and the reference arm is
dithered to generate a heterodyne signal by the interference with the