Applications of a Confocal Scanning Laser Holography (CSLH) instrument for measuring the three-dimensional temperature of a fluid and transparent objects Peter B. Jacquemin ⇑ , Rodney A. Herring 1 University of Victoria, Department of Mechanical Engineering, 3800 Finnerty Road, BC, Canada V8P 5C2 article info Article history: Received 7 June 2011 Received in revised form 15 March 2012 Available online 12 April 2012 Keywords: Confocal Microscope Holography Laser Reconstruction Three-dimensional abstract 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 refrac- tive 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 k/10 wave fringe shift resolution in the hologram. The reconstructed temperature res- olution is 1 °C in three-dimensions by processing the experiment data. The CSLH concept and tomo- graphic 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. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The concept of combining confocal microscopy and holography into one microscope for 3D phase imaging of objects was first pub- lished in 1997 by Herring [1]. A holographic microscope records the amplitude and phase of an object or all of the information of light as compared to an optical microscope which is sensitive to only the amplitude or intensity of light. The specimen of a standard optical microscope absorbs spectral energy which omits the phase properties and sensitivity to refractive index. The hologram of the CSLH microscope is a measure of the cumu- lative effects of refractive index as the laser propagates through the specimen. A phase-shift is represented by a fringe translation in a hologram which is due to a change in refractive index. The refrac- tive index relates to the wave velocity within the medium or spec- imen and the optical path length through the specimen. The confocal aspect of the CSLH microscope reduces beam aberrations at the image plane while providing high resolution three- dimensional scanning of the object using a specific optical geometry that was developed by Dixon et al. [2]. The holography aspect of the CSLH microscope provides a measurement of the object’s phase which is used to determine the object’s refractive index. The phase of the object is reconstructed into index-of-refraction values and then converted to temperature based on the optical properties of the fluid. The point spread function of the focused laser within the spec- imen is 170 lm in diameter as determined by Zemax lens design software of the optical train and by measurement during the experiment phase. The scan-to-scan positional increment is 625 lm/step which provides for independent resolution within the computational grid spacing of 625 lm in three-dimensions (voxel size). Multiple scanned holograms are then combined to reconstruct a 3D refractive index of the object. Measurements of laser interaction with the specimen represent through the thickness cumulative effects which appear on the sen- sor or hologram. The cumulative refractive index along the path length through the specimen is commonly known as the Radon line integral as found in tomographic reconstruction. Scanning the laser in three-dimensions within the specimen is performed in this experiment and in Hossain and Shakher [3]. Hossain and Shakher [3] addresses phase unwrapping but can only produce an average temperature throughout the depth of the specimen. Tieng and Chen [4] applies a modified simultaneous algebraic reconstruction technique to reconstruct the three-dimensional temperature for aerodynamic flow but specifies the sensitivity to error based on geometric configuration. The CSLH microscope 0017-9310/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2012.03.039 ⇑ Corresponding author. Tel.: +1 (250) 743 6780. E-mail addresses: pbj@uvic.ca (P.B. Jacquemin), rherring@uvic.ca (R.A. Herring). 1 Tel.: +1 (250) 721 8934 (office); fax: +1 (250) 721 6051. International Journal of Heat and Mass Transfer 55 (2012) 4020–4028 Contents lists available at SciVerse ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt