The availability of high-power blue diode-lasers established a new class of laser sources for materials processing recently. With the significantly shorter wavelength compared to conventional laser sources for materials processing new applications are moving into the range of the feasible. There is a strong demand for welding applications with copper due to the change from internal combustion engines to electric drives, which even prompts laser manufacturers to find complex solutions to obtain a laser source in the wavelength range where copper shows higher absorption. With the appearance of high-power diode-laser bars in the blue wavelength range, proven optical concepts can be adapted for the setup of straightforward blue high-power diode-laser sources for materials processing. In context of the research project “BlauLas”, which is funded by the German Federal Ministry of Education and Research (BMBF) within the photonic initiative “EFFILAS” , Laserline, in cooperation with OSRAM, intends to realize a blue fiber-coupled cw diode-laser with a power exceeding 1 kW. Building on the results of the earlier presented 700 W fiber coupled laser source we present our new blue fiber coupled laser source with output powers surpassing 1 kW. A brief description of the optical concept and setup as well as an outlook on future strategies to increase output power and radiance of blue laser sources based on diode-laser bars are given. Additionally recently carried out application trials with this new powerful laser source are presented.
Proc. SPIE. 10514, High-Power Diode Laser Technology XVI
KEYWORDS: Semiconductors, High power lasers, Copper, Materials processing, Laser applications, Semiconductor lasers, High power diode lasers, Fiber coupled lasers, Laser systems engineering, High power fiber coupled lasers
A high-power blue laser source was long-awaited for processing materials with low absorption in the near infrared (NIR) spectral range like copper or gold. Due to the huge progress of GaN-based semiconductors, the performance of blue diode-lasers has made a major step forward recently. With the availability of unprecedented power levels at cw-operating blue diode-lasers emitting at 450 nm, it was possible to set up a high-power diode-laser in the blue spectral range to address these conventional laser applications and probably beyond that to establish completely new utilizations for lasers.
Within the scope of the research project “BlauLas”, funded within the German photonic initiative “EFFILAS”  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.
Industrial material processing like cutting or welding of metals is rather energy efficient using direct diode or diode pumped solid state lasers. However, many applications cannot be addressed by established infrared laser technology due to fundamental material properties of the workpiece: For example materials like copper or gold have too low absorption in the near infrared wavelength range to be processed efficiently by use of existing high power laser systems. The huge interest to enable high power kW systems with more suitable wavelengths in the blue spectral range triggered the German funded research project 'BLAULAS': Therein the feasibility and capability of CW operating high power laser bars based on the GaN material system was investigated by Osram and Laserline.
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.
In this paper we present the next step on the roadmap “system scalability towards an output power above 100 kW”, first
time presented in 2014 .
To take a step forward the optical power of the fiber-coupled diode laser has been increased beyond the power level
40kW. The power conversion efficiency exceeds 40%. The laser contains modules with 4 different wavelengths (960nm,
1020nm, 1040nm, 1060nm) there are two modules for each wavelength polarization multiplexed. After the slow-axis
collimation these wavelengths are combined using dense wavelength coupling before focusing onto the fiber endface.
The delivery-fiber is an uncoated fiber with a diameter of 2 mm and NA 0.22 corresponding a BPP of 220 mm mrad.
In a stability test the laser delivered a constant maximum output power with less than ±0.5 % variation over 100h.
Further results of the optical properties of the laser will be presented in this paper.
This new laser is based on a turn-key industrial platform, allowing straight-forward integration into almost any industrial
application, like welding or large area heat treatment. As application examples laser welding of thick sheet metal and
pumping of an active fiber will be presented. The footprint of the complete system is 2.8 m² with a height below 1.8 m.
In this paper we report the development of a new fiber-coupled diode laser for pumping applications capable of generating 25 kW with four wavelengths. The delivery fiber has 2.0 mm core diameter and 0.22 NA resulting in a Beam Parameter Product (BPP) of 220 mm mrad. To achieve the specifications mentioned above a novel beam transformation technique has been developed combining two high power laser stacks in one common module. After fast axis collimation and beam reformatting a beam with a BPP of 200 mm mrad x 40 mm mrad in the slow and fast-axis is generated. Based on this architecture a customer-specific pump laser with 25 kW optical output power has been developed, in which two modules are polarization multiplexed for each wavelength (980nm, 1020nm, 1040m and 1060nm). After slow-axis collimation these wavelengths are combined using dense wavelength coupling before focusing onto the fiber endface. This new laser is based on a turn-key platform, allowing straight-forward integration into any pump application. The complete system has a footprint of less than 1.4m² and a height of less than 1.8m. The laser diodes are water cooled, achieve a wall-plug efficiency of up to 60%, and have a proven lifetime of <30,000 hours. The new beam transformation techniques open up prospects for the development of pump sources with more than 100kW of optical output power.