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 “frozen” 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.
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Abbreviations
- λ :
-
wavelength
- x, y :
-
cartesian coordinate system
- Φ :
-
phase
- ΔΦ :
-
phase step
- K :
-
Gladstone-Dale constant
- L :
-
width of 2-D density field
- ϱ :
-
density
- ϱ 0 :
-
density at reference conditions
- I 0, I 1, I 2, I 3 :
-
recorded interferograms
- I mod :
-
modulation intensity
- I bias :
-
bias intensity
- N :
-
numerator determining tan {ϱ (x, y)}
- D :
-
denominator determining tan {ϕ (x, y)}
- θ :
-
dimensionless temperature
- T :
-
temperature
- T c :
-
temperature of cylinder
- T ∞ :
-
temperature of environment
- p :
-
pressure
- R :
-
gas constant
References
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Lanen, T.A.W.M., Nebbeling, C. & van Ingen, J.L. Digital phase-stepping holographic interferometry in measuring 2-D density fields. Experiments in Fluids 9, 231–235 (1990). https://doi.org/10.1007/BF00190424
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DOI: https://doi.org/10.1007/BF00190424