Dynamic measurement of 2D refractive index distribution of NaCl solutions

Abstract

We demonstrate a simple and reliable method for measuring the two-dimensional refractive index (RI) distribution of transparent liquids, either homogeneous or inhomogeneous. The RI variation and the RI over the laser incident surface are measured by computing the phase shift of the interferograms as the optical path difference between the two beams passing through the sample liquid and air is changing. The phase shift is calculated by analyzing the interferograms by fast Fourier transform and a fringe shift counter. The RI change of the NaCl–water in the dissolving process was successfully measured by our method. This algorithm is stable, fast, efficient and of high accuracy up to 10⁻⁴. It holds potential for some applications that requires noncontact, and particularly for inhomogeneous transparent mediums.

Keywords:

• Interferometry
• fringe analysis
• phase measurement
• refractive index measurement

Acknowledgements

The author would like to thank Prof Zhengdong Cheng of Texas A&M University for helpful discussion and comments on this paper.