Mie scattering as a technique for the sizing of air bubbles

A technique has been developed which allows the radius of a bubble in a fluid to be accurately measured without disturbing the bubble. Results are presented which show that radius measurements of single air bubbles in water can be achieved by shining a He–Ne laser on the bubble and measuring the light scattered at 80°. Light intensity measurements at a scattering angle of 55° were used to calibrate a photodiode detection system and to demonstrate the correlation of data with Mie scattering theory. The photodiode was then moved to 80° for actual radius measurements. This technique was accurate to within 3% for bubbles with radii of <80 μm.