UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2019 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
The study of the properties of water droplets using a Mach-Zehnder interferometer and Mie rigorous diffraction


Authors:
Petre Cătălin LOGOFĂTU, Florin GAROI, Mihai BONI, Mihail Lucian PASCU


Affiliation:
National Institute for Laser, Plasma and Radiation Physics, Laser Dept., str. Atomiștilor nr. 409, CP MG-36, Măgurele, jud. Ilfov, Romania, 077125


E-mail
petre.logofatu@inflpr.ro


Keywords:
water droplet, Mach-Zehnder interferometry, Mie rigorous diffraction, Fresnel diffraction, interference pattern sensitivity to heating


Abstract:
We studied theoretically and experimentally the interference pattern of a water droplet placed in the object arm of a Mach-Zehnder interferometer, and the influence of droplet heating [1] on it. It turns out that due to special circumstances, the diffraction pattern of the sphere in the shadow area is particularly insensitive to changes of refractive index [2], because it is identical to the Fresnel diffraction of an opaque disc in the shadow area [3]. However, this pattern is sensitive to changes of the droplet volume caused by dilation, which is another effect of the heating. We were able to formulate a sui-generis Babinet principle valid in these special circumstances. More promising turns out to be the back and lateral Mie scattering [4]. The interference pattern in this case is sensitive to droplet heating at certain angles, although the two effects of the heating on the droplet - the refractive index change and the dilation [2,5] - tend to compensate each other. Scanning the scattering angle for sensitivity provides measurement configurations where the two effects of heating are uncoupled. Lateral and back Mie scattering measurements are difficult, because the signal is weak and the interference pattern is sensitive to vibrations since the interfringe is small, but they are feasible [6]. Further interference experiments with the heated droplet using the Fizeau interferometer are in work.


References:

1. A. R. Glover, S. M. Skippon, and R. D. Boyle, “Interferometric laser imaging for droplet sizing: a method for droplet-size measurement in sparse spray systems,” APPLIED OPTICS Vol. 34, No. 36 pp 8409 (1995).

2. Alexey N. Bashkatov , Elina A. Genina, „Water refractive index in dependence on temperature and wavelength: a simple approximation” Saratov Fall Meeting 2002: Optical Technologies in Biophysics and Medicine IV, Valery V. Tuchin, Editor, Proceedings of SPIE Vol. 5068 (2003).

3. Joseph W. Goodman, “Introduction to Fourier optics” 4t ed, MacMillan, New York (2017).

4. Max Born and Emil Wolf, „Principles of Optics”, Cambridge University Press, Cambridge (1999).

5. https://physics.info/expansion/

6. Petre Cătălin Logofătu, Ioan Ardelean, Dan Apostol, Iuliana Iordache, Mihaela Bojan, Cristina Moisescu, and Bogdan Ioniţă, „Determination of the magnetic moment and geometrical dimensions of the magnetotactic bacteria using an optical scattering method” JOURNAL OF APPLIED PHYSICS 103, 094911 (2008).