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Digital phase-stepping holographic interferometry in measuring 2-D density fields
Authors:T. A. W. M. Lanen  C. Nebbeling  J. L. van Ingen
Affiliation:(1) Dept. of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, P.O. Box 5058, NL-2629 HS Delft, The Netherlands
Abstract:This paper presents a holographic interferometer technique for measuring transparent (2-D or quasi 2-D) density fields. To be able to study the realization of such a field at a certain moment of time, the field is ldquofrozenrdquo on a holographic plate. During the reconstruction of the density field from the hologram the length of the path traversed by the reconstruction beam is diminished in equal steps by applying a computer controlled voltage to a piezo-electric crystal that translates a mirror. Four phase-stepped interferograms resulting from this pathlength variation are digitized and serve as input to an algorithm for computing the phase surface. The method is illustrated by measuring the basically 2-D density field existing around a heated horizontal cylinder in free convection.List of symbols lambda wavelength - x, y cartesian coordinate system - PHgr phase - DeltaPHgr phase step - K Gladstone-Dale constant - L width of 2-D density field - rhov density - rhov0 density at reference conditions - I0, I1, I2, I3 recorded interferograms - Imod modulation intensity - Ibias bias intensity - N numerator determining tan {rhov (x, y)} - D denominator determining tan {phiv (x, y)} - theta dimensionless temperature - T temperature - Tc temperature of cylinder - Tinfin temperature of environment - p pressure - R gas constant
Keywords:
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