Abstract
Large-area processing with high material removal rates by ultrashort pulsed (USP) lasers is coming into focus by the development of high-power USP laser systems. However, currently the bottleneck for high-rate production is given by slow and inefficient beam manipulation. On the one hand, slow beam deflection with regard to high pulse repetition rates leads to heat accumulation and shielding effects, on the other hand, a conventional focus cannot provide the optimum fluence due to the Gaussian intensity profile. In this paper, we emphasize on two approaches of dynamic laser beam shaping with liquid crystal on silicon spatial light modulation and acousto-optic beam shaping. Advantages and limitations of dynamic laser beam shaping with regard to USP laser material processing and methods for reducing the influence of speckle are discussed. Additionally, the influence of optics induced aberrations on speckle characteristics is evaluated. Laser material processing results are presented correlating the achieved structure quality with the simulated and measured beam quality. Experimental and analytical investigations show a certain fluence dependence of the necessary number of alternative holograms to realize homogeneous microstructures.
Highlights
An increase of productivity represents a significant challenge to transfer ultrashort pulsed (USP) laser based microstructuring processes into industrial application
Homogeneity of flat-top profiles is achieved for N = 36 and N = 12 added holograms in LCoS-SLM and acousto-optic beam shaping (AOS) beam shaping
Simulation results of LCoS-SLM-based flat-top profiles show that stagnation and absolute value of the speckle contrast are nearly independent from optical aberrations
Summary
An increase of productivity represents a significant challenge to transfer ultrashort pulsed (USP) laser based microstructuring processes into industrial application. 111 Page 2 of 9 system technologies and methods for beam shaping of flattop profiles with flexible contours are highly relevant In this context, liquid crystal on silicon spatial light modulation (LCoS-SLM) and acousto-optic beam shaping (AOS) are addressed in this paper. Liquid crystal on silicon spatial light modulation (LCoS-SLM) and acousto-optic beam shaping (AOS) are addressed in this paper Both methods enable flexible holographic beam shaping due to the local variation of the phase of the laser beam. LCoS-SLM is based on the individual manipulation of the refractive index of pixels of a liquid crystal display, while acousto-optic beam shaping (AOS) is based on a fast variation of an acoustic wave enabling a spatially dependent phase variation of laser beams. The AOS technology enables wavefront shaping [11] for 3D nonlinear microscopy [12] and intensity profile shaping [13]
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