Focusing elements and system for producing a prescribed energy distribution along an axial focal zone

An optical playback system for reading data from a record includes a focusing system for focusing a scanning light beam onto data on the record without need for precision positioning of the record and optical elements of the system. The light beam is modulated by the data and then transmitted to a light detector to produce a playback data signal corresponding to the recorded data. The focusing system includes a source of light having an axially symmetric intensity distribution and a lens designed to focus such light into a focal zone with a specified intensity distribution along the zone. This distribution is preferably uniform so as to provide the detector with a modulated light beam of uniform average intensity regardless of the position of the record along to focal zone . The lens is but one member of an entire family of nonconical, aspherical axicon-type focusing elements designed in accordance with a method described herein to focus energy from given source to a prescribed focal zone intensity distribution.