Adaptive extracavity beam shaping for application in nanosecond laser micromachining

The typical Gaussian intensity distribution generated at focus of a laser machining workstation is not always ideal for the application; instead other shapes such as ellipses, flat-tops (circular or square), or doughnuts can in some cases give better results. Also, other more complex beam profiles might be beneficial for surface micro structuring. In order to realise, and rapidly change between such beam shapes, we are investigating an adaptive optics approach based on using an iterative simulated annealing algorithm to control the actuators of a deformable mirror. A 37-element piezoelectric deformable mirror and a 37-element bimorph mirror were applied in an extracavity arrangement. Beam shaping results with these systems are presented and example laser machining is demonstrated in this paper. The results enabled by the deformable mirrors are compared to previous results using a spatial light modulator (SLM) based on a liquid crystal microdisplay. The SLM has a much higher resolution and enables complex beam shapes to be generated, however is much slower in response. Having an active beam shaping element incorporated in a laser machining workstation adds increased flexibility and improves process control. © 2011 SPIE.