Applications of a Confocal Scanning Laser Holography (CSLH) instrument for measuring the three-dimensional temperature of a fluid and transparent objects

► 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. The Confocal Scanning Laser Holography (CSLH) microscope was designed to measure the temperature distribution of a fluid in three dimensions using a focused laser beam. The laser beam passes through the specimen and is interfered with a reference beam to form a hologram. The minute changes in refractive index produce fringe-shifts in a hologram. The fringe-shifts are converted to temperature, pressure, or composition depending on the configuration. A tomographic reconstruction algorithm, which is based on the numerical aperture of the beam, was derived for the microscope. Narrow field angle scanning is restricted to the numerical aperture or cone angle of the laser beam probing the specimen which increases the error in determining the three-dimensional properties of a specimen. The holography aspect of the microscope preserves the phase of the object which provides a temperature sensitivity of 0.1°C based on a λ/10 wave fringe shift resolution in the hologram. The reconstructed temperature resolution is 1°C in three-dimensions by processing the experiment data. The CSLH concept and tomographic reconstruction method of hologram data can be applied to precise non-invasive measurement of displacement, temperature, pressure, and composition of thick regions with positional resolution near the wavelength of the laser beam. Micro-fluidics and other areas of research and applied technology may well consider the unique measurement benefits of the CSLH device.