DIODE LASERS
THE DIRECT APPROACH
Greg Blackman investigates the advances being made in direct diode lasers and asks whether these systems can compete with fibre lasers
F 10
ibre lasers, some would argue, are now the dominant laser technology in metal cutting, but take away the fibre architecture to leave the diode pump source, and this should be a
much less expensive and more efficient way of producing laser light, right? In principle, yes, but it depends on the beam quality required, according to Dr Jens Biesenbach, CTO of Coherent-Dilas – the company makes laser diodes and was part of Rofin until the group was purchased by Coherent earlier in the year. Diode lasers are generally considered to have
poor beam quality – at least compared to a fibre laser – so putting too much effort into combining diode lasers and maintaining the highest possible beam quality will add cost, for example in the beam shaping optics. ‘Tere’s a certain break-even
LASER SYSTEMS EUROPE ISSUE 33 • WINTER 2016
point where beam quality and power is more economical to produce in a direct diode laser than a fibre laser,’ Biesenbach observed. Poor beam quality has been a feature of the
diode laser in the past, but now higher brightness systems, operating at kilowatt powers, are finding their way into the marketplace and beginning to compete with fibre lasers in terms of beam quality. Teradiode, a start-up from MIT in the US, is one company producing these high brightness diode systems. It claims a beam parameter product of 3mm-mrad from a fibre-coupled direct diode laser with an output power of 2kW, equal to a brightness of 2,293 MW/cm2
–sr. Te company
also offers kilowatt-class direct diode lasers for metal processing with a brightness of 6,800MW/ cm2
–sr, which equals that of comparable fibre
lasers, according to its website. Japanese machine tool builder Mazak is one of
the early adopters of Teradiode’s technology for sheet metal cutting. At Fabtech in Las Vegas in November, Mazak was demonstrating a direct diode machine – using Teradiode’s laser technology – side by side with a fibre laser. In the demonstration, a 4kW Mazak direct diode system was able to cut 9mm stainless steel
44 per cent faster than a 4kW fibre laser. Te same diode system cut 1mm copper 50 per cent faster than the fibre laser. It was 10 per cent faster cutting 9mm mild steel; 18 per cent faster cutting 1mm aluminium; and 14 per cent faster cutting 1mm stainless steel. ‘Across all material types and thicknesses up to
9mm, the 4kW direct diode laser was faster than a 4kW fibre laser,’ commented Rajiv Pandey, senior product line manager at Teradiode. Te Mazak Optiplex 3015 direct diode machine
was also displayed at Euroblech in Germany in October. Panasonic adopted Teradiode’s technology
around two years ago for its welding machines; metal welding has been earlier in adopting high brightness diode technology, because the process doesn’t require as high a beam quality as cutting. ‘By expanding into the cutting and welding markets, we’re taking market share from fibre lasers and, as the market grows, we will grow with the market,’ Pandey said. Teradiode’s technology is based on wavelength
beam combining. It uses a diffraction grating to merge multiple wavelength sources into a single, high-intensity beam.
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