Interferometric measurement of diffusion coefficients through a scanning laser beam

Elvio Alanis; Graciela Romero; Carlos C. Martinez

doi:10.1117/1.602422

1 March 2000 Interferometric measurement of diffusion coefficients through a scanning laser beam

Elvio Alanis, Graciela Romero, Carlos C. Martinez

Optical Engineering, Vol. 39, Issue 3, (March 2000). https://doi.org/10.1117/1.602422

A new interferometric setup for the determination of the concentration distribution in a diffusion experiment is proposed. The method is applied to the determination of the diffusion coefficient D in a binary saline solution. A thin laser beam scans the diffusion cell along the concentration gradient, which is assumed to be one-dimensional. This beam interferes with the reference beam in a Mach-Zehnder interferometer, and the variation of intensity is recorded by means of photomultiplier tube, digitized, and stored in a computer for further analysis. The phase of the intensity function, modulo 2?, is determined by applying the Fourier-transform method. Assuming linear dependence of the refraction index on the concentration, the unwrapped phase gives a curve similar to the theoretical concentration distribution function. The value of the diffusion coefficient D is obtained by means of an iterative process, comparing experimental and theoretical curves until the best fit is achieved between them, by adjusting the parameter D.

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Elvio Alanis, Graciela Romero, and Carlos C. Martinez "Interferometric measurement of diffusion coefficients through a scanning laser beam," Optical Engineering 39(3), (1 March 2000). https://doi.org/10.1117/1.602422

Published: 1 March 2000

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