RECENT theory1–3 and experiments4–7 have demonstrated the existence of an intensity dependent non-linear component in the refractive index of some materials. This non-linearity in the refractive index has been observed to rotate an elliptically polarized optical maser beam4,5 and to lead to self trapping6,7. This communication considers the two step nature of focusing which leads to the conclusion that a sample tank filled with one of these non-linear materials can be made to behave like a lens. It will be shown that it is possible for beam trapping to occur within the non-linear medium but for the beam to come to a focus outside the medium tank (see Fig. 1).