High power diode laser line generators are nowadays industrial standard for applications like plastic processing, vision
inspection and drying. With increased beam quality, especially peak intensity and homogeneity, they also enable new
applications like hardening, annealing or cutting of various materials. All of these applications have in common that
simultaneous processing is limited by the scalability of the generated line length without changing process relevant
parameters of the line like working distance, peak intensity, homogeneity and depth of focus. Therefore, a patent pending
beam shaping concept is presented that enables the interconnection of an arbitrary number of nearly free selectable laser
sources to generate scalable laser lines with outstanding beam parameters. System design, experimental setup and results
of a laser line generator are shown. It is based on a stitching concept consisting of ten fibre coupled high power diode
lasers, which generates a 200mm long and 2mm wide laser line with a homogeneity level of 97% p-v over a depth of
focus of +/- 5 mm with an overall output power of up to 4.2 kW. The concept is discussed regarding industrial
applications and the options for even higher beam quality, especially the capability of generating lines with increased
power densities up to several kW/cm² and a line length of several meters.
Beam shaping improvements of line generators based on high power diode lasers in combination with newly designed and produced high precision micro-optics lead to new applications such as hardening, metallization and annealing of different materials.
Two aspects are mainly needed to be focused on for getting the best results and throughput in these applications. The first one is the overall power content along the narrow axis of the line, namely the peak intensity in combination with the beam shape. The second one is the intensity homogeneity along the long axis of the line.
Herewith, a beam shaping concept that fulfils the desired requirements in a variable modality is presented. The concept
consists of macro-lenses and newly designed micro-optics and results in a passively cooled high power diode laser emitting at 808nm. The laser has an output power of 1000W. The generated line has a length of 13mm and a width of <100μm at a remarkably large working distance of about 80mm. We attained an intensity distribution along the line length with a peak power density >80kW/cm2 and uniformity >97%. To achieve such an extraordinary homogeneity level, several approaches based on cylindrical lens arrays were designed and tested. Methods to reduce inhomogeneities caused by diffraction effects and effects based on geometric optics are presented as well as their results. Additionally, the potential of this concept with regard to modularity, expandability and variability is reviewed.
Finally, an application example - crystallisation of a thin film of a-Si on a glass substrate - is presented.
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