FEATURE DIODE LASERS
Jenoptik’s high- power diode lasers for industry and medicine
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“The most advanced diode lasers are those that can be produced using automated means at high yield and high quality, and which are modular and scalable in power”
20 Electro Optics November 2017
much more complex and costly to maintain the beam quality of a diode laser compared to a fibre laser. ‘Today, the fibre laser, with its all-fibre architecture, is a more cost- effective beam improver for diode lasers than multiple, complex optical elements for wavelength stabilisation and the beam multiplexing of many hundreds of single 100μm cavities,’ Biesenbach said. This latter approach still cannot achieve the beam parameter product of a fibre laser at high powers, he added. In the last few years, according to Biesenbach, the output power per 100μm emission of a single diode laser cavity increased beyond 10W – for this, multi- emitters are produced in a single monolithic bar. In addition, higher brightness – comparable to the beam quality of lamp- pumped solid-state lasers (20 mm x mrad) – has been achieved using Coherent Dilas’ tailored-bar (TBar) technology. In this way, 4kW output can be achieved with a diode laser. Biesenbach noted that, for welding applications, the results, in terms of speed and metal thickness, are comparable with a fibre laser. Coherent Dilas’ TBar concept was
developed during a 42-month EU project aimed at increasing the brilliance of direct diode laser systems, BRIDLE (Brilliant
Industrial Diode Lasers), which concluded in 2016. The tailored bar diode laser concept allows the fabrication of a laser source that is high-brightness, scalable in power and economic to produce. According to Biesenbach, it combines the advantages of both the single emitter and bar-based diode lasers: reliability, high power per element, efficient cooling, compactness, and handling of several emitters in a monolithic chip at one time throughout production. ‘So, power and brightness are improving
in parallel now, which shows we are on a good path to service more high brightness applications, which so far were only addressed by solid-state or fibre lasers,’ Biesenbach noted. However, he added that the complexity needs to be reduced by integrating, for example, wavelength stabilising technology on the chip or wafer level, which is required for collecting the output power of multiple emitters via dense wavelength multiplexing. ‘This complexity needs to be lower than using an active fibre as a beam enhancer for the diode laser, as it is typically done in a fibre laser,’ he said.
Cutting metal Some diode systems are already being used for high-power industrial applications. One company, Teradiode, a MIT spin-off that’s
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Jenoptik/Stefan Marquardt.
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