Optical Gaussian-to-tophat converters (g2T) that convert a Gaussian intensity distribution into a tophat profile find growing applications in different laser processing technologies. Usually, such refractive or diffractive g2T converters comprise of two or more optical components. For example, one aspherical component to form a tophat angular distribution followed by a Fourier lens that transforms it into the desired tophat intensity distribution in the focal plane. Here we report an optical design, which combines both optical functions in a single monolithic component. The component is designed and manufactured by LIMO as a free-form profile, providing the square tophat of 100-μm width at the distance of 125 mm. Compared to the traditional g2T-converters it is much more compact, easy to adjust, and less sensitive to alignment errors. In many industrial applications, not a single but multiple tophat foci are desirable for a fast parallel processing. For such applications we have developed a Gaussian-to-Tophat beam splitter. The beam splitting is done by a refractive-diffractive high-order grating with a smooth continuous pitch profile. Thanks to the smooth profile, such a Gaussian-to- Tophat beam splitter demonstrates very high efficiency of above 95% and high homogeneity between the diffraction orders.
Fiber-coupled diode lasers have become an established source for many industrial applications due to their high wall-plug
efficiency, minimal maintenance and cost per watt. To decrease system size and cost for cooler and driver, high
coupling efficiencies have become more and more important.
Recent developments in broad area laser diode bars (BALB) and beam shaping systems with micro-optical components
are leading to new highly efficient fiber coupling.
We present newly developed high power diode laser modules which are performing at outstanding efficiencies with
smallest package design. The combination of recently designed laser diode bars on passive heat sinks and optimized
micro-optics results in laser modules with up to 60W out of a 200μm fiber with a 0.22 NA and > 50% electro-optical
efficiency out of the fiber core, based on only one laser diode bar.
The applications for such laser diode modules range from pumping of fiber lasers and amplifiers, over materials
processing to medical applications.
The presentation of the technology will show a path to scale high-brightness laser systems to higher power levels and
efficiencies. The combination of different coupling techniques will allow laser modules with 100W out of 100μm fiber
core up to 1.6kW out of 400μm fiber core with electro-optical efficiencies of > 45%.
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.