sentences:  Micrometer sized (from several to 50 micrometers in diameter) transparent dielectric spheres such as fused silica spheres, oil or water droplets, are used in this type of experiment.The laser radiation can be fixed in wavelength such as that of an argon ion laser or that of a tunable dye laser.Laser power required is of the order of 1 Watt focused to a spot size of several tens of micrometers.