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On the other side, new applications may occur in the near future. We will present research data on blue laser bars as a possible component for industrial applications like for materials processing. LIV characteristics are measured up to power levels of 107W. We observe power conversion efficiencies of 44% at 60W output power for our best samples.
For cw laser bars, we report on efficiency improvements to further increase the output power beyond today’s power limits for reliable operation with 250 W. For long term use under q-cw conditions, we show a very cost effective approach using a 1.5 mm cavity, capable to provide 500 W. For sensing applications we report on 200 μm wide emitters providing 130 W of pulsed power, based on monolithically stacked laser structures.
Within the scope of the research project “BlauLas”, funded within the German photonic initiative “EFFILAS” [8] by the German Federal Ministry of Education and Research (BMBF), Laserline in cooperation with OSRAM aims to realize a cw fiber-coupled diode-laser exceeding 1 kW blue laser power.
In this paper the conceptual design and experimental results of a 700 W blue fiber-coupled diode-laser are presented. Initially a close look had to be taken on the mounting techniques of the semiconductors to serve the requirements of the GaN laser diodes. Early samples were used for extensive long term tests to investigate degradation processes. With first functional laser-modules we set up fiber-coupled laser-systems for further testing. Besides adaption of well-known optical concepts a main task within the development of the laser system was the selection and examination of suitable materials and assembling in order to minimize degradation and reach adequate lifetimes. We realized R&D blue lasersystems with lifetimes above 5,000 h, which enable first application experiments on processing of various materials as well as experiments on conversion to white-light.
We also report on a new approach based on 450 nm diode laser bars, which dramatically reduces size and alignment effort. These activities were performed within the German government-funded project “BlauLas”: a maximum output power of 80 W per bar has been demonstrated @ 450 nm. We show results of a 200 μm NA0.22 fiber coupled 35 W source @ 450 nm, which has been reduced in size by a factor of 25 compared to standard single emitter approach. In addition, we will present a 200 μm NA0.22 fiber coupled laser unit with an output power of 135 W.
High performance bars were enabled by defeating fundamental challenges like material quality as well as the chip processes, both of which differ significantly from well-known IR laser bars. The research samples were assembled on actively cooled heat sinks with hard solder technology. For the first time an output power of 98W per bar at 60A drive current was achieved. Conversion efficiency as high as 46% at 50W output power was demonstrated.
We present results on the improvement of T-Bars tailored for optimized coupling into fibers with a diameter of 200 μm with NA 0.22 corresponding to a beam parameter product of 22 mm·mrad. Cost efficient coupling to this fiber requires a tailored beam parameter product smaller than 15.5 mm·mrad in slow axis direction corresponding to a slow axis beam divergence of 7° (full angle, 95% power content) for five 100 μm wide emitters. The improved T-Bars fulfil this requirement up to an output power of 52 W with a brightness of 3.1 W/mm·mrad and a power conversion efficiency achieving 69%. This progress in the T-Bar performance together with modifications in the module design led to the increase of the reliable output power from 135 W in 2009 to 360 W in 2017 for a T-Bar module with one baseplate. We will also give a review of the main development steps and further R and D improvements.
We present results on the improvements of the lateral beam divergence and brightness of gain-guided mini-bars for emission at 976 nm. For efficient fiber coupling into a 200 μm fiber with NA 0.22, the upper limit of the lateral beam parameter product is 15.5 mm mrad. Within the last years, the power level at this beam quality has been improved from 44 W to 52 W for the chips in production, enabling more cost efficient pump modules and laser systems.
Our work towards further improvements of the beam quality focuses on advanced chip designs featuring reduced thermal lensing and mode shaping. Recent R&D results will be presented, showing a further improvement of the beam quality by 15%. Also, results of a chip design with an improved lateral emitter design for highest brightness levels will be shown, yielding in a record high brightness saturation of 4.8 W/mm mrad.
Measurement and simulation of the lateral mode profile of broad ridge 405 nm (Al,In)GaN laser diodes
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