Explosive lens

An explosive lens—as used, for example, in nuclear weapons—is a highly specialized shaped charge. In general, it is a device composed of several explosive charges. These charges are arranged and formed with the intent to control the shape of the detonation wave passing through them. The explosive lens is conceptually similar to an optical lens, which focuses light waves. The charges that make up the explosive lens are chosen to have different rates of detonation. In order to convert a spherically expanding wavefront into a spherically converging one using only a single boundary between the constituent explosives, the boundary shape must be a hyperboloid; similarly, to convert a spherically diverging front into a flat one, the boundary shape must be a paraboloid, and so on. Several boundaries can be used to reduce aberrations (deviations from intended shape) of the final wavefront.