Gaussian-to-top-hat beam shaping: an overview of parameters, methods, and applications

Abstract

Direct laser patterning of various materials is today widely used in several micro-system production lines like inkjet printing, solar cell technology, flat-panel display production, LEDs, OLEDs, semiconductors and medicine. Typically single-mode solid state lasers and their higher harmonics (e. g. 266, 355, 532 and 1064 nm) are used especially for machining of holes and grooves. The striking advantages of flat top intensity distributions compared to Gaussian beam profiles with respect to the efficiency and quality of these processes were already demonstrated. Here we will give an overview of parameters, methods and applications of Gaussian-to-top-hat beam shaping. The top hat field size can start from about 30 µm with no upper size limitation in the far field of the optics. Beam shaping for various wavelengths were realized with field geometries of squares, rectangles and circles. With LIMO's compact Gaussian-to-top-hat converter an inhomogeneity better than 5% contrast was reached. Special focus is put on the integration of Gaussian-to-top-hat beam shapers in fast scanning systems employing Galvo mirrors and a specially developed f-Theta lens to avoid destruction of the top hat profile within the scan field. Results with a 50x50μm² top hat size (inhomogeneity down to <10%) in a scan area of 156x156mm² are presented. The minimal distortions of the top hat observed within the scan area make LIMO's compact Gaussian-to-top-hat converter excellently suited for industrial scanning applications, e.g. for the processing of solar panels.

Quantum-limited estimation of the axial separation of two incoherent point sources

“…Here we only take into account the 0th and 1st order radial modes in calculating the Fisher information of LG mode sorter and Zernike mode sorter, which should be reasonably achievable in an experiment. Moreover, given the widely used Gaussian-to-tophat laser beam shaper [65,66], it is possible to convert the pupil function of a hard-edged aperture to a Gaussian and then apply the radial mode sorter subsequently. Recent advances in multi-plane light conversion [67] also provide an alternative possible solution for building a Zernike mode sorters.…”

Effects of Top-hat Laser Beam Processing and Scanning Strategies in Laser Micro-Structuring

“…The latest beam shaping solutions fall into two main groups [1,[17][18][19][20][21][22], i.e., multifaceted beam integrators based on reflective phase elements and field mapping employing diffractive and refractive optical element. The multifaceted beam integrators can be of different types, e.g., micro-lens arrays, spatial light modulator (SLM), or multi-plane light conversion (MPLC).…”

“…Thus, this increases the heat affected zone (HAZ) while decreasing the processing efficiency of delivered pulse energies. Therefore, an energy redistribution across the beam spatial profile through the use of beam shapers can minimize and even avoid the pulse tail and, thus, achieving the desired intensity distribution at the laser spot [1]. In particular, Gaussian spatial intensity can be transformed into top-hat, donut, or reverse Gaussian distribution by employing beam shapers.…”

Extending the limits of laser beam shaping for PV-cell manufacturing

“…Lab experiments have demonstrated the advantages of using a Gaussian-to-top hat converter to process photovoltaic cells 1,2 . The next step to qualify this technology for industrial production is an improvement of process stability and speed.…”