Multi spot optics are used for parallelizing production and therefore enabling large-scale material processing. These
elements split the beam into a periodic spot pattern with a defined grid and spot size. The challenge lies in the generation
of a homogeneous envelope. Micro lens arrays offer a high flexibility in dimensions and shapes for the generation of
different multi spot patterns.
Within the paper we present the investigation of a micro lens array in a fly's eye condenser setup for the generation of
homogeneous spot patterns. The principal functionality of the multi spot generator is shown and constraints of this setup
are demonstrated. The multi spot generator is used for micro structuring of silicon with a nanosecond and a picosecond
laser both at a wavelength of 355 nm. The multi spot generator splits the incoming beam into a linear spot matrix with 28
single spots. The ablation rate and structure quality using a multi spot generator are investigated compared to
conventional treatment. It can be shown, that both ablation efficiency and structure quality can be increased by using a
multi spot generator.
Multi focus optics are used for parallelizing production and for large-scale material processing. These elements split the
beam into a periodic spot pattern with a defined grid and spot size. The challenge lies in the generation of a
homogeneous envelope. Additionally the demand for flexible systems for an in-process changing of optical properties
increases. Different components for multi spot generation like diffractive optical elements or micro lens arrays have been
investigated. Diffractive optical elements offer large degree of freedom in the generation of arbitrary intensity
distributions. In the paper we demonstrate the use of a diffractive element in combination with a multi spot generator.
Within the paper we present the investigation of a micro lens array in a fly's eye condenser setup for the generation of
homogeneous spot patterns. The multi spot generator is combined with a galvanometer scanner for forming an arbitrary
shaped laser beam into a spot-, ring or arbitrary array pattern. We show the principal functionality of the multi-spot
generator. Furthermore constrains of this setup are demonstrated. The multi spot scanner is used for micro structuring of
silicon with a nanosecond diode pumped solid state laser. The ablation rate and structure quality are compared to single
spot processing.
Laser manufacturing of microstructures using a single focus is a well known technology. Multi-spot optics are applied
for process parallelizing if the demand on throughput in mass production rises or large areas of material have to be
processed. Diffractive optical elements (DOEs) are used for parallel laser processing of a repetitive structure. These
elements split the beam into a periodic spot pattern, where each spot shows the same shape and energy. This allows
simultaneous manufacturing of several equal shaped structures at the same time. For patterning a surface this is state of
the art and the appropriate technique to reduce processing time while maintaining a high lateral resolution as well as a
good relative positioning of the structure due to the DOE.
We investigate the usage of microlens arrays as multifunctional elements for forming an arbitrary shaped laser beam into
a spot-, a ring-spot- or a line-array pattern. It can be shown that the intensity distribution of each spot is equal to the
intensity distribution of all other spots in the whole pattern. The shape of the spots is defined by the angular distribution
of the incident beam. We demonstrate that besides other optical properties the output beam profile strongly depends on
the Fresnel-Number and is influenced by diffraction and interference effects. We present important design rules which
consider geometrical and physical optics. The properties of the spot arrays, like spot diameter, Rayleigh length and beam
divergence in dependency of beam and system properties are investigated. Finally we will show some laser micro
structuring and micro drilling results in different materials.
Refractive, diffractive and reflective micro-optical elements for laser beam shaping and homogenizing have been manufactured and tested. The presented multifunctional optical elements are used for shaping arbitrary laser beam profiles into a variety of geometries like, a homogeneous spot array or line pattern, a laser light sheet or flat-top intensity profiles. The resulting profiles are strongly influenced by the beam properties of the laser and by diffraction and interference effects at the micro-optical elements. We present general design rules for beam shaping and homogenizing. We demonstrate the application of such multifunctional micro-optical elements for a variety of applications from micro-laser machining to laser diagnostic systems.
Many applications in laser manufacturing like semiconductor lithography, micro-machining, micro-structuring or
material-analysis require a homogeneous intensity distribution of the laser beam over its complete profile. Refractive and
diffractive beam homogenizer solutions have been developed for this challenge, but their applicability strongly depends
on the physics of the individual laser beam. This paper investigates the influence of laser beam properties like spatial
coherence for microlens beam homogenizers. Diffraction at the small lens apertures and interference effects of periodic
arrays are explained by using diffraction theory. Different microlens beam homogenizer configurations are presented.
Design considerations that might be helpful for the layout of a specific microlens beam homogenizer system are
discussed. It is shown that, among other factors, the Fresnel number is the most important quantity to characterize the
influence of diffraction effects on microlens laser beam homogenizers. The influence of the spatial partial coherence will
be explained for the example of a Fly's eye condenser. For cw laser sources, the influence of a rotating diffuser plate on
grating interference and speckles effects is investigated. Finally, the theory will be compared to some practical examples
in planar laser measurement techniques, in combustion diagnostics and micromachining with Excimer lasers.
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