Selmke, M.M.Selmke2022-03-062022-03-062020https://publica.fraunhofer.de/handle/publica/26121410.1364/AO.59.000045Starting from a peculiar image observed below a bubble that is floating at a water-air interface, this paper analyzes several optical properties of these special types of refracting objects (termed bubble axicons). Using mainly geometrical optics, their relation to common axicons, the shadow-sausage effect, and elementary optical catastrophes (caustics) are discussed.en620535journal article