Turbidity data obtained from image analysis in near critical hydrogen.

Abstract

Video images are being used with increased frequency in science, supplanting current methods such as light scattering by statistical evaluation of the images. In this study we use light turbidity data due to density-induced refractive index fluctuations to obtain critical amplitudes from image analysis. In order to bring hydrogen (H_{2}) very close to its critical point, we place the sample cell under weightlessness using a magnetic levitation device. Images of an H_{2}-filled cell are taken near its critical temperature of 33 K by illuminating the cell with three different filters. We fit the turbidity data to a theoretical expression that allows us to estimate the critical amplitudes of isothermal compressibility and fluctuation correlation length. The values of isothermal compressibility and correlation length obtained from turbidity fitting are compared against literature values. Our data analysis shows a large sensitivity of the fitting parameters to the refractive index value and to even minute density deviations from criticality.