A novel method for optical bubble-sizing

Although a number of optical methods for bubble-sizing already exist, e.g. photography and holography, they suffer from the disadvantage that a number of time-consuming steps are involved between taking the image and analysing it. Furthermore, exposure times and shutter speeds are often a matter of trial and error, and the process of analysing the results is tedious and therefore error-prone. The authors propose a method which will allow in situ real-time measurements of the spatial bubble size distribution of a bubble screen or cloud to be performed. The method involves looking at fringes produced by laser light scattered from individual bubbles. Although this technique has been used before by Langley and Marston (l984), the present authors propose employing spatial filters and an optical correlator to automate the identification of bubble sizes. analysis shows that this method will apply to bubbles with radii ranging from about 1O μm up to 1 mm or 2 mm, to an accuracy of a few per cent