Laser autofocusing: a sliding mode approach

Quality of the laser processing depends on many factors, such as overall configuration of the laser workstation, control methods used and quality of the laser beam. Although lasers used in material processing are typically high energy lasers, light beam still needs to be focused in order to achieve higher energy density and smaller final spot size. This paper presents an application of sliding mode to the laser autofocusing system. Autofocusing system consists of photodiode as the measurement element, focusing lens and pilot laser beam. Photodiode is saturated and measurement is done in the nonlinear region of the responsivity curve. Problem of limited knowledge about the photodiodes behavior in this region is solved through sliding mode minimization algorithm. Verification of the proposed method is done experimentally.