Holographic interferometry measurement of refractive index and concentration of liquids
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Date
2014-10-07
Authors
Irungu, Joseph Mburu
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
The refractive index (n) is a basic optical property of materials and its accurate value is often
needed in many branches of physics and chemistry. Measurement of liquid concentration is
important in fields such as chemical analysis and processing, diagnostics, and semiconductor
manufacturing. Refi•actometers are used routinely to evaluate the refractive index to determine
concentration of liquid mixtures. Still other techniques reported for accurately measuring the
refractive index of solids and gases include the minimum deviation method, the use of a Littrow
prism, Brewster angle techniques and others. All these techniques, however suffer from one or
more of the following shortcomings: they must get in contact with the liquid, have poor
resolution, require complicated and expensive components, are physically large and difficult to
operate, or rely on a visual, subjective measurement of data. Despite the use of infi•ared ethanol
sensors to determine the concentration of alcohol which measure the vibrational frequency of
dissolved ethanol, this technique only makes use of light intensity only losing the effect of the
phase. Holographic interferometry invo Ives a phase object interfering with a memory of itself at
a preceding time, recorded on a hologram. Interference fringes therefore inform on any variation
of the phase of the object. A holographic interferometry technique will be used in the
measurement of the concentration and refractive index of liquid mixtures and solutions. The
essential components in the system include a He-Ne laser (632.8nm) as the light source, a
precision glass cuvette as the liquid container and optical cell, a holographic plate and digital
camera. The work involves taking three of the common alcohols (Ethanol, Methanol and
Propano I) and distilled water each into a cuvette and recording their holograms separately. The
distilled water hologram is taken as a reference hologram and the concentration of the alcohol is
varied and poured in the cuvette for reconstruction. The interferogram obtained during
reconstruction wi II be captured using a CCD camera. The captured interferogram wi II be
analyzed for the measurement of the concentration and refractive index of liquid. The analysis
will be replicated for ethanol, methanol, propanol, distilled water and water mixtures. Further
analysis will be conducted using Fourier transform infrared spectroscopy (FTIR) and the results
compared with those obtained from the holographic interferometry method