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.

[1]  Andrew Waddie,et al.  Application of cooled spatial light modulator for high power nanosecond laser micromachining. , 2010, Optics express.

[2]  R. Gerchberg.  A practical algorithm for the determination of phase from image and diffraction plane pictures , 1972 .

[3]  Klaus H. Kudielka,et al.  Low-Order Adaptive Optics System for Free-Space Lasercom: Design and Performance Analysis , 1999 .

[4]  Peter Rossmanith,et al.  Simulated Annealing , 2008, Taschenbuch der Algorithmen.

[5]  R El-Agmy,et al.  Adaptive beam profile control using a simulated annealing algorithm. , 2005, Optics express.

[6]  M. Murnane,et al.  Adaptive pulse compression for transform-limited 15-fs high-energy pulse generation. , 2000, Optics letters.

[7]  Rajesh S. Patel,et al.  Highest-speed dicing of thin silicon wafers with nanosecond-pulse 355nm q-switched laser source using line-focus fluence optimization technique , 2010, LASE.

[8]  O B Vyskubenko,et al.  Application of deformable mirrors in industrial CO2 lasers. I. A mirror with a controllable curvature of the reflecting surface , 2003 .

[9]  E N Ribak,et al.  Simulated annealing in ocular adaptive optics. , 2006, Optics letters.

[10]  G. Stoilov,et al.  Phase-stepping interferometry: Five-frame algorithm with an arbitrary step , 1997 .

[11]  M Montes-Usategui,et al.  Design strategies for optimizing holographic optical tweezers set-ups , 2007, physics/0701037.

[12]  Derryck T. Reid,et al.  Direct optimization of femtosecond laser ablation using adaptive wavefront shaping , 2007 .

[13]  Ian Elder,et al.  End-pumped Q-switched Nd:YVO4 laser , 2006, SPIE Security + Defence.

[14]  Constance Valentin,et al.  Adaptive shaping of a focused intense laser beam into a doughnut mode , 2005 .

[15]  Ping Yang,et al.  Adaptive Laser Beam Shaping Using a Genetic Algorithm , 2007, 2007 International Conference on Mechatronics and Automation.

[16]  G. Mourou,et al.  Smart microscope: an adaptive optics learning system for aberration correction in multiphoton confocal microscopy. , 2000, Optics letters.