High power diode laser line generators are nowadays industrial standard for applications like plastic processing, vision
inspection and drying. With increased beam quality, especially peak intensity and homogeneity, they also enable new
applications like hardening, annealing or cutting of various materials. All of these applications have in common that
simultaneous processing is limited by the scalability of the generated line length without changing process relevant
parameters of the line like working distance, peak intensity, homogeneity and depth of focus. Therefore, a patent pending
beam shaping concept is presented that enables the interconnection of an arbitrary number of nearly free selectable laser
sources to generate scalable laser lines with outstanding beam parameters. System design, experimental setup and results
of a laser line generator are shown. It is based on a stitching concept consisting of ten fibre coupled high power diode
lasers, which generates a 200mm long and 2mm wide laser line with a homogeneity level of 97% p-v over a depth of
focus of +/- 5 mm with an overall output power of up to 4.2 kW. The concept is discussed regarding industrial
applications and the options for even higher beam quality, especially the capability of generating lines with increased
power densities up to several kW/cm² and a line length of several meters.
High power laser sources are used in various production tools for microelectronic products and solar cells, including the
applications annealing, lithography, edge isolation as well as dicing and patterning. Besides the right choice of the laser
source suitable high performance optics for generating the appropriate beam profile and intensity distribution are of high
importance for the right processing speed, quality and yield.
For industrial applications equally important is an adequate understanding of the physics of the light-matter interaction
behind the process. In advance simulations of the tool performance can minimize technical and financial risk as well as
lead times for prototyping and introduction into series production. LIMO has developed its own software founded on the
Maxwell equations taking into account all important physical aspects of the laser based process: the light source, the
beam shaping optical system and the light-matter interaction.
Based on this knowledge together with a unique free-form micro-lens array production technology and patented micro-optics
beam shaping designs a number of novel solar cell production tool sub-systems have been built. The basic
functionalities, design principles and performance results are presented with a special emphasis on resilience, cost
reduction and process reliability.
Beam shaping improvements of line generators based on high power diode lasers lead to new application fields as
hardening, annealing or cutting of various materials.
Of special interest is the laser treatment of silicon. An overview of the wide variety of applications is presented with
special emphasis of the relevance of unique laser beam parameters like power density and beam uniformity.
Complementary to vision application and plastic processing, these new application markets become more and more
important and can now be addressed by high power diode laser line generators.
Herewith, a family of high power diode laser line generators is presented that covers this wide spectrum of application
fields with very different requirements, including new applications as cutting of silicon or glass, as well as the beam
shaping concepts behind it. A laser that generates a 5m long and 4mm wide homogeneous laser line is shown with peak
intensities of 0.2W/cm2 for inspection of railway catenaries as well as a laser that generates a homogeneous intensity
distribution of 60mm x 2mm size with peak intensities of 225W/cm2 for plastic processing. For the annealing of silicon
surfaces, a laser was designed that generates an extraordinary uniform intensity distribution with residual
inhomogeneities (contrast ratio) of less than 3% over a line length of 11mm and peak intensities of up to 75kW/cm2.
Ultimately, a laser line is shown with a peak intensity of 250kW/cm2 used for cutting applications. Results of various
application tests performed with the above mentioned lasers are discussed, particularly the surface treatment of silicon
and the cutting of glass.
High power laser sources are used in a large variety of applications for material processing, such as ablation, welding,
soldering, cutting, drilling, laser annealing, micro-machining and deep-UV lithography. Using high performance optics
in the laser systems to generate the appropriate beam profile becomes a key factor for getting the best results and
throughput in an application field. Refractive micro-lens arrays made of glass, semiconductors or crystals provide great
advantages in laser applications, by improving efficiency, precision, intensity stability and performance.
With LIMO's unique production technology, free form surfaces on monolithic arrays exceeding 200 mm edge length can
be manufactured with high precision and reproducibility. Each lens of the array can be designed individually and can
also be shaped asymmetrically. The asymmetric shape is defined by
odd- and even-polynomial terms and/or an
asymmetric cut-off from a polynomial surface. Advantages of asymmetric micro-lenses are off-axis light propagation,
the correction of aberration effects, or the correction of the intensity profile deformations when the illuminated surfaces
are not orthogonal to the optical axis.
The applications results of such micro-lens arrays are presented for beam shaping of high power diode lasers. The
generation of a homogeneous light field by a 100 W laser with tilted illumination under an angle of 30°-50° is shown. A
multi-kW line generator based on the superposition of over 50 diode laser bars under different illumination angles is
demonstrated as well.
Novel microoptical beam shapers in lithographic applications reduce the complexity of macrooptics in hyper-NA illumination systems. Extremely uniform intensity distribution can be created without using field lenses or by using simple spherical field lenses instead of complex aspheres.
Beam shaping improvements of line generators based on high power diode lasers in combination with newly designed and produced high precision micro-optics lead to new applications such as hardening, metallization and annealing of different materials.
Two aspects are mainly needed to be focused on for getting the best results and throughput in these applications. The first one is the overall power content along the narrow axis of the line, namely the peak intensity in combination with the beam shape. The second one is the intensity homogeneity along the long axis of the line.
Herewith, a beam shaping concept that fulfils the desired requirements in a variable modality is presented. The concept
consists of macro-lenses and newly designed micro-optics and results in a passively cooled high power diode laser emitting at 808nm. The laser has an output power of 1000W. The generated line has a length of 13mm and a width of <100μm at a remarkably large working distance of about 80mm. We attained an intensity distribution along the line length with a peak power density >80kW/cm2 and uniformity >97%. To achieve such an extraordinary homogeneity level, several approaches based on cylindrical lens arrays were designed and tested. Methods to reduce inhomogeneities caused by diffraction effects and effects based on geometric optics are presented as well as their results. Additionally, the potential of this concept with regard to modularity, expandability and variability is reviewed.
Finally, an application example - crystallisation of a thin film of a-Si on a glass substrate - is presented.
We present newly developed high power diode laser modules which are performing at outstanding power densities and line uniformity. The combination of recently designed laser diode bars on passive heat sinks and optimized micro-optics results to laser modules with power densities > 100kW/cm2 in a line length of 12mm x 0.1mm. The usage of non periodic structured homogenizers leads to a homogeneity of less than 3% p/v which allows precise heating and annealing applications. The application for such laser lines are hardening, metallization and annealing of different materials. In the presentation we will show results of thin film Si-a annealing process with direct diode laser annealing.
KEYWORDS: Beam shaping, High power diode lasers, Homogenization, Semiconductor lasers, Lenses, Laser sources, Manufacturing, Laser processing, High power lasers, Semiconductors
Micro-lens arrays are widely used for beam shaping, especially beam homogenization of various laser sources.
Monolithic arrays of cylindrical lenslets made of glass, semiconductors or crystals provide great advantages in laser
applications, e.g. high efficiency, intensity stability and very low absorption. However, up to now, mainly symmetrical
micro-lens surfaces are utilized in most applications due to design and manufacturing restrictions. The manufacture and
application benefits of asymmetrical cylindrical-like micro-lens surfaces are enabled by LIMO's unique production
technology. The asymmetrical shape is defined by uneven-polynomial terms and/or an asymmetrical cut-off from an
even polynomial surface. Advantages of asymmetrical micro-lenses are off-axis light propagation, the correction of
aberration effects or intensity profile deformations when the illuminated surfaces are not orthogonal to the optical axis.
Additionally, the opportunities in simultaneous illumination from numerous light sources to one target are extended by
just geometrical arrangement without the need for collinear beam alignment. First application results of such micro-lens
arrays are presented for beam shaping of high power diode lasers. The generation of a homogeneous light field by a 100
W laser with tilted illumination at an angle of 35° is shown. A multi-kW line generator based on the superposition of
over 50 diode laser bars under different illumination angles is demonstrated as well. Thus, laser material processing like
plastics welding, soldering or annealing becomes much more convenient and less demanding regarding beam steering.
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