An increase in the performance of micro-optic beam shaping resulted in diode laser modules with more than 400W out
of 200 μm fibre based on Broad Area Laser Bars (BALB). The brightness of a 400 W laser module opened the door for
new applications in material processing such as temper marking of stainless steel and metal sheet cutting.
Further improvements of the light sources and the beam shaping for BALB's have increased the efficiency of the laser
Therefore we present an output power of 1200 W out of a 200 μm fibre (0.22 NA). This is achieved by further
sophistication of the coupling technique and four wavelength coupling. The beam parameter product is still 22
mm*mrad with a power density of 3800 kW/cm<sup>2</sup> if focussed to a 200 μm spot. Furthermore, each of the four
wavelength modules are separately exchangeable and checkable.
The availability of a top-hat profile out of the fibre proves itself to be advantageous compared to the traditional
Gaussian beam profiles of fibre, solid-state and gas lasers. This leads to excellent laser cutting results with extremely
small cutting kerfs down to 200 μm and very plane cutting edges. Process speeds rise up to more than 10 m/min i.e. for
thin sheet stainless steel or titanium. In the near future, 600 W out of 200 μm based on BALB's with a beam compressor
is possible. With wavelength coupling, power levels with up to 2 kW out of 200 μm fibre will be reached. This will
result in a power density of more than 6 MW/cm<sup>2</sup>.
So far, diode laser systems could not compete against CO<sub>2</sub>-lasers or DPSSL in industrial applications like marking or
cutting due to their lower brightness. Recent developments in high-brightness diode laser bars and beam forming
systems with micro-optics have led to new direct diode laser applications.
LIMO presents 400W output from a 200μm core fibre with an NA of 0.22 at one wavelength. This is achieved via the
combination of newly designed laser diode bars on passive heat sinks coupled with optimized micro-optical beam
shaping. The laser is water cooled with a housing size of 375mm x 265mm x 70mm.
The applications for such diode laser modules are mainly in direct marking, cutting and welding of metals and other
materials, but improved pumping of fibre lasers and amplifiers is also possible. The small spot size leads to extremely
high intensities and therefore high welding speeds in cw operation. For comparison: The M<sup>2</sup> of the fibre output is 70,
which gives a comparable beam parameter product (22mm*mrad) to that of a CO<sub>2</sub> laser with a M<sup>2</sup> of 7 because of the
Many metals have a good absorption within the wavelength range of the laser diodes (NIR, 808nm to 980nm), which
permits the cutting of thin sheets of aluminium or steel with a 200W version of this laser. First welding tests show
reduced splatters and pores owing to the optimized process behaviour in cw operation with short wavelengths.
The availability of a top-hat profile proves itself to be advantageous compared to the traditional Gaussian beam profiles
of fibre, solid-state and gas lasers in that the laser energy is evenly distributed over the working area.
For the future, we can announce an increase of the output power up to 1200W out of a 200μm fibre (0.22 NA). This will
be achieved by further sophistication and optimisation of the coupling technique and the coupling of three wavelengths.
The beam parameter product will then remain at 22mm*mrad with a power density of 3.8 MW/cm<sup>2</sup> if focussed to a
200µm spot. This leads to excellent laser cutting results with extremely small cutting kerfs down to 200μm and very
plane cutting edges. Process speeds rise up to more than 10m/min i.e. for thin sheets of stainless steel or titanium.
Current laser systems based on high-power laser diode bars need active cooling either water cooling or the use of
thermo-electric coolers to ensure an adequate operating temperature for a reasonable lifetime. Here is a solution with a
bonded fin heat sink and forced ventilation introduced, a diode laser bar with an improved efficiency and a low thermal
resistance as well as an optical system for a highly efficient fibre coupling. With this system it is possible to couple 25
Watt continuous wave power from a single laser diode bar on a passive heat sink into a fibre with 200 μm core
The basis for this performance is a heat sink with an exceptionally low thermal resistance. Several new features are
introduced to reach a low overall gradient between the laser diode temperature and the ambient temperature. In addition,
it does geometrically fit to the layout of the optical design. Shape and aspect ratio of both heat sink and housing of the
laser system are matched to each other. Another feature is the use of hard-soldered or pressed bars to achieve a thermo-mechanically
stable performance. The long-term thermal characteristic was tested. The operation temperature comes to
saturation after about 30 minutes. Therefore it can be used for continuous wave operation at 25 Watt output power. At a
quasi continuous operation at 70 percent duty cycle a peak power of 30 Watt out of the fibre is possible.
From this technology results a compact fibre coupled laser system what is simple to drive compared with current high
power laser systems, because there is no need to control the operating temperature. This gives way for more compact
driver solutions. Fields of application are laser marking systems and material processing, where a simple driver system
is requested. Also medical applications need this requirement and a compact cooling too so that mobile integrated
solutions become possible. Further developments allow multiple laser diode systems for specific industrial applications
demanding more power. Our measurements show the potential for direct air-cooled laser systems with 100 Watt power
out of the fibre.