A low error reconstruction method for confocal holography to determine 3-dimensional properties

A confocal holography microscope developed at the University of Victoria uniquely combines holography with a scanning confocal microscope to non-intrusively measure fluid temperatures in three-dimensions [1] (Herring, 1997), [2] (Abe and Iwasaki, 1999), [3] (Jacquemin et al., 2005). The Confocal Scanning Laser Holography (CSLH) microscope was built and tested to verify the concept of 3D temperature reconstruction from scanned holograms. The CSLH microscope used a focused laser to non-intrusively probe a heated fluid specimen. The focused beam probed the specimen instead of a collimated beam in order to obtain different phase-shift data for each scan position. A collimated beam produced the same information for scanning along the optical propagation z-axis. No rotational scanning mechanisms were used in the CSLH microscope which restricted the scan angle to the cone angle of the probe beam. Limited viewing angle scanning from a single view point window produced a challenge for tomographic 3D reconstruction. The reconstruction matrices were either singular or ill-conditioned making reconstruction with significant error or impossible. Establishing boundary conditions with a particular scanning geometry resulted in a method of reconstruction with low error referred to as “wily”. The wily reconstruction method can be applied to microscopy situations requiring 3D imaging where there is a single viewpoint window, a probe beam with high numerical aperture, and specified boundary conditions for the specimen. The issues and progress of the wily algorithm for the CSLH microscope are reported herein.

► Evaluation of an optical confocal holography device to measure 3D temperature of a heated fluid.
► Processing of multiple holograms containing the cumulative refractive index through the fluid.
► Reconstruction issues due to restricting angular scanning to the numerical aperture of the beam.
► Minimizing tomographic reconstruction error by defining boundary conditions.