Reproducibility of radiant energy measurements inside light scattering liquids

Resumo

The aim of this project is to evaluate the uncertainty associated with measurements performed with laser beams in scattering liquids with optical fibers. Two lasers with different wavelengths were used, 632.8 nm and 820 nm, to illuminate a cuvette with Lipovenos PLR, the scattering liquid. A mask at the top of the cuvette was used to control the positioning of 250 µm optical fiber and the laser entrance point. The light energy was measured with an optical power meter, and the integration time was 60 s, measured with a chronometer. There were no systematic errors associated with the integration time. Two tests were done to evaluate the uncertainty associated with the positioning of the components of the experimental arrangement. To evaluate the uncertainty of the positioning of the cuvette, seven series of measurements with the optical fiber 5 mm far from the beam were performed. Between two series, the cuvette was removed from the holder, the liquid was mixed and the cuvette was put back in the same position. A second test was done to evaluate the reproducibility of fiber positioning and the relative positioning of mask and cuvette. Three distances between the beam and the fiber were used: 4 mm, 5 mm and 6 mm, through the positioning of the fiber at three different holes in the mask. Six series of measurements were performed. Between two series, the cuvette was removed from the holder, the liquid was mixed and the cuvette was put back in the same position. Each series was done in a different order, permuting the three positions. The uncertainty associated with the positioning of the experimental elements was of the order of 7%. The variation of incident laser energy was also evaluated, resulting in 6.5% and 4.0% for the red and infrared lasers respectively