Optical detection of small changes in refractive indices in water by single-beam scattering

We studied forward-scattered laser light that is produced when the light st rikes an abrupt interface (air bubble in water) and when it passes unimpede d through diffused water layers caused by temperature gradients. Measured i ntensities of the scattered light indicated patterns that are due to both g eometrical and physical optics. Distribution of intensities within the scat tered beam changed with the average vertical temperature gradient. Shifts i n locations of intensities indicated small changes in the index of refracti on in the diffused scattering case. (C) 2001 Optical Society of America.