  Scanning laser confocal holographic microscopy using a spatial heterodyne
detection method is presented. Spatial heterodyne detection technique employs a
Mach-Zehnder interferometer with the reference beam frequency shifted by two
acousto-optic modulators (AOM) relative to the object beam frequency. Different
from the traditional temporal heterodyne detection technique in which hundreds
temporal samples are taken at each scanning point to achieve the complex
signal, the spatial heterodyne detection technique generates spatial
interference fringes by use of a linear tempo-spatial relation provided by
galvanometer scanning in a typical line-scanning confocal microscope or for the
slow-scanning on one dimension in a point-scanning confocal microscope, thereby
significantly reducing sampling rate and increasing the signal to noise ratio
under the same illumination compared to the traditional temporal heterodyne
counterpart. The proposed spatial heterodyne detection scheme applies to both
line-scanning and point-scanning confocal microscopes. In this paper, we
present the mathematical principles of the spatial heterodyne detection method
and experimental schemes for both line-scanning and point-scanning confocal
microscopes. Computer experiments are provided to demonstrate the validity of
this idea. The presented spatial heterodyne scanning laser confocal holographic
microscope (SH-SLCHM) can obtain both amplitude and quantitative phase
information of the object field without a significant increase in complexity of
optical and electronic design on the basis of a traditional scanning laser
confocal microscope (SLCM). SH-SLCHM may find applications in optical
metrology, in-vivo tissue imaging, and ophthalmic imaging.
