Adaptive optics for laser processing
Abstract
The overall aim of the work presented in this thesis is to develop an adaptive optics
(AO) technique for application to laser-based manufacturing processes. The Gaussian
beam shape typically coming from a laser is not always ideal for laser machining.
Wavefront modulators, such as deformable mirrors (DM) and liquid crystal spatial light
modulators (SLM), enable the generation of a variety of beam shapes and furthermore
offer the ability to alter the beam shape during the actual process.
The benefits of modifying the Gaussian beam shape by means of a deformable mirror
towards a square flat top profile for nanosecond laser marking and towards a ring shape
intensity distribution for millisecond laser drilling are presented. Limitations of the
beam shaping capabilities of DM are discussed.
The application of a spatial light modulator to nanosecond laser micromachining is
demonstrated for the first time. Heat sinking is introduced to increase the power
handling capabilities. Controllable complex beam shapes can be generated with
sufficient intensity for direct laser marking. Conventional SLM devices suffer from
flickering and hence a process synchronisation is introduced to compensate for its
impact on the laser machining result. For alternative SLM devices this novel technique
can be beneficial when fast changes of the beam shape during the laser machining are
required. The dynamic nature of SLMs is utilised to improve the marking quality by
reducing the inherent speckle distribution of the generated beam shape. In addition,
adaptive feedback on the intensity distribution can further improve the quality of the
laser machining.
In general, beam shaping by means of AO devices enables an increased flexibility and
an improved process control, and thus has a significant potential to be used in laser
materials processing.