System Technology and Process Control (LiM 2017)

Observing process zone temperature fields for process characterization
Volpp, Joerg; Hohenäcker, Viktor; Tyralla, Dieter; Freiße, Hannes; Brocke, Nils; Silze, Frank; Schnick, Michael; Thomy, Claus

Thermal processes like welding or additive manufacturing are standard applications in industrial process chains. Using the laser as a heat source can increase e. g. processing speed and energy efficiency. Process results can suffer from sudden changes of process parameters which can induce unwanted pores, spatters, insufficient connection or blow holes. The temperature fields of the material surface can be used to detect process changes and imperfections already during the process. However, optical temperature measurements of thermal processes can be difficult, as the emissivity of the material in the process zone varies depending on temperature changes, melting or even vaporization. In order to guarantee efficient high quality processes for industrial applications a process observation of the temperature is necessary. Therefore, emissivity compensated temperature measurement systems are evaluated in order to determine their suitability to measure the temperature fields during laser materials processing applications for the detection of process variations. The target application investigated in this paper is laser cladding. Temperature measurements with a standard RGB-camera and a pyrocamera show that the melt pool width can be determined. Process variations of powder application, velocity and focal position can be distinguished from the temperature field.

Keywords: Temperature field analysis; Laser materials processing; Additive manufacturing; Laser cladding


Laser joining improvement and prediction of the quality of the joint of metal-composite samples using a control and supervision system for temperature and clamping force
Andrés, Maite; Liébana, Fernando; Ferros, Mercedes; Villarón, Iker; Ukar, Eneko

Joining of multi-material parts is a growing need for development components with enhances properties. Laser
conduction joining is a promising alternative but still a relatively unexplored technique for joining dissimilar metal-
composite materials. As a thermal joining method, the achieved temperature is one of the most influent parameters on
the strength of the joint and mainly depends on laser power, speed, material and geometry of the part, meanwhile the
clamping force guarantees the heat conduction from the metallic specimen to the composite material. For this reason,
the supervision and control of these parameters are especially relevant to ensure the quality of the joint. This paper is
focused on the development of a control and supervision system of these parameters for the improvement of the
process and the prediction of the joint quality. The system has been evaluated through on purpose production of
defective joints for the validation of the reliability of the process with different metal-composite combinations.

Keywords: process control; process supervision; composite-metal laser joining; multi-material laser joining; quality prediction;


Power Management of Randomly Modulated and Pulsed Laser Systems
Bystryak, Ilya

Laser System integrators are constantly faced with the necessity of optimization of electrical part of a
system. This is especially difficult with randomly modulated and pulsed laser systems. Very often an
electrical system has to handle tens (hundreds) of kilowatts of pulse power while average power
consumption does not exceed small fraction of that level. Q-switched diode lasers, randomly modulated
laser diode based systems, CO2 lasers (in super-pulse mode), RF pumped CO2 lasers and flash lamp pumped
lasers are good examples of such kind of systems.
Usually, an intermediate energy storage device (capacitor) is used to mitigate high power needs but an
electronics system intended to replenishing the energy in the intermediate storage device does not get
deserved attention. As a result, the supply line experiences uneven power consumption, high peak currents
and system generates a lot of electromagnetic noise (EMI). This, in turn, creates control and communication
Supply power lines or DC sources (batteries) are supposed to see only average power consumption. This is
especially important for battery powered systems.
This presentation is an attempt to address these issues and demonstrate that the power consumption
averaging system is the path to laser system optimization for performance, efficiency, cost and size.

Keywords: System Technology, Process Control, Pulse Power, Efficiency, System Integration.


Laser beam shape monitoring as a quality control tool in material processing
Harrop, Nick; Schwede, Harald; Haensel, Klaus G.

In the early days of laser processing, monitoring the laser beam quality was done by cardboard or Plexiglas mode burns. More advanced technologies for laser beam diagnostics like scanning systems or camera based systems were developed and introduced into the market, providing higher quality and reproducibility of laser beam analysis as well as giving the potential of quality traceability during product accruement and product life time. Two laser beam caustic measuring concepts will be discussed to show the potential of today’s laser beam analysis. The OnlineBeamMonitor OBM is a camera based, processing head integrated caustic measurement system. The system uses backscattered laser light coming from the protective window of the processing head. Using zoom optics, a complete caustic of the focused laser beam can be measured. During material processing, the backscattered light can be used for simultaneous control of the laser beam quality. The measurement system is directly linked with the laser controller. Evaluation and computation of the measured values will be done in a short timeframe to keep the system updated about the actual spot size and position. The new FocusMonitor FM+ is system independent. In combination with the new LaserDiagnosticSoftware LDS, monitoring the laser beam quality becomes quicker and easier using automated measuring cycles, fast Ethernet interface and advanced software tools for computation, evaluation and analysis of measured laser beam data. The complete beam caustic can be measured automatically and the characteristic beam parameters like spot diameter, Rayleigh length, beam quality M², divergence among will be evaluated from the measurement results. The benefits of laser beam monitoring in an industrial environment will be discussed. Hereby, a main aspect is the excellent integration capability of measuring device and software into existing data processing networks.

Keywords: Laser Power Measurement, Process Monitoring, Beam Diagnostics, Quality Control


Transformation of weld seam geometry in laser transmission welding by using an additional integrated thulium fiber laser
Schmailzl, Anton; Geißler, Bastian; Maiwald, Frederik; Laumer, Tobias; Schmidt, Michael; Hierl, Stefan

Laser transmission welding is a well-known joining technique for thermoplastics. By using a single laser source with a wavelength close to one micron, the laser radiation is transmitted through the upper joining partner almost loss-free and afterwards absorbed in the below placed absorbent polymer. By this, the majority of the molten volume of the weld seam is located in the below placed joining partner. Furthermore, the melt layer thickness in the upper joining partner is reduced in regions with an initial gap, because heat conduction is precluded in the beginning of the welding procedure. As a result, the weld seam quality varies along the weld contour. In the worst case a gap is remaining, which causes a leakage. In order to enhance the weld seam quality, a laser with a wavelength close to two micron can be used additionally. By this, a significant absorption is given in the upper joining partner, whereby gap bridging is accelerated due to thermal expansion of the upper joining partner. In this approach, a thulium fiber laser with a wavelength of 1.94 micron is used in a coaxial arrangement to a conventionally used diode laser. Welding experiments on extruded polyamide plates are performed using several different process parameter settings, whereby typical feed rates for the process variants contour and quasi-simultaneous welding are used. It is shown, that the geometry of the weld seam can be easily manipulated, by adapting the power density distribution of the thulium fiber laser. Verification studies for both process variants have shown that computational and experimental results are matching with adequate accuracy,
especially for several different process parameter settings. In order to investigate the correlation between weld seam geometry and strength in further studies, the simulation can be used as a quick and reliable tool.

Keywords: laser transmission welding; gap bridging, thulium fiber laser, process simulation, hybrid welding


New approach for all-in-one control of galvanometer scanners
Rauscher, Peter; Schwarz, Thomas; Hauptmann, Jan; Wetzig, Andreas; Beyer, Eckhard

A new approach to connect scanners directly with a standard PLC (Programmable Logic Controller) with the advantages of the openness, flexibility and real-time communication of industrial fieldbus system will be presented. The main advantage is a connection of all for the specific laser application necessary sensors and actors within one control solution. We present a communication module, which was developed to realize the communication between the industrial fieldbus system EtherCAT and the digital scanner protocol SL2-100. The possibilities of the device will be discussed on selected example.

Keywords: scanner control; remote technology; remote laser processing;


Optical monitoring of fiber laser based cutting processes for in-situ quality evaluation
Ocaña, Roberto; Garmendia, Iker; Soriano, Carlos; Lambarri, Jon

In this study we present a simple experimental set-up for optical monitoring of cutting processes with fiber laser. The
developed sensor uses two Si-photodiodes, each attached to four optical fibers that collect radiation at four symmetrical
off-axis orientations around the processing zone. The photodiodes allow monitoring the scattered light from both sides
of the sample regardless of the cutting direction. The development allows easy change of the filters as well as the
photodiodes in order to monitor different spectral ranges. In this study we focus on a narrow range around the
wavelength of the processing laser. At the top of the sample the photodiode signal is related to scattering processes at
the sample surface and processing zone. The photodiode shows a constant behaviour when the process parameters give
rise to a high quality cut and either saturates or presents noisy oscillations when irregular or incomplete cutting is
obtained. At the bottom of the sample, the collected radiation contains information about the exact penetration time as
well as laser scattering by the ejected material during the cutting process. An analysis of both signals allows to resolve
non-optimal effects such as cutting tears/burrs or incomplete cut zones. In addition, a correlation with the overall
cutting quality can be established. This characteristic would allow in-situ process controlling in industrial production

Keywords: Monitoring; fiber laser; laser cutting; photodiode; quality control.


Realization and first time operation of a high-power laser-water-jet system
Schmidt, Florian; Brecher, Christian; Janssen, Henning

Micromachining industry successfully uses the advantageous properties of laser-water-jets (LWJ), e.g. high depth of
field, cooling and cleaning effect of water as well as high kerf parallelism. Until now short-pulsed laser sources with
average powers of few 100 W are the main beam sources used in laser-water-jets applications. In machining, the
comparably low average powers limit processing speeds, especially when high material thicknesses are present.
The objective of ongoing research at Fraunhofer IPT is to expand the range of possible applications for laser-water-jets
to macro laser processing by using a continuous-wave fiber laser source with a maximum average power of 30 kW. Using
high laser power within a macro-water-jet enables a significant increase in processing speeds while maintaining the
above-mentioned beneficial properties of laser-water-jets. In a previous publication, using up to 2 kW laser power of an
infrared fiber laser coupled in a laser-water-jet generated by an industrial micro machining system, the need for a
dedicated high-power laser system, capable of dealing with thermo-optical and thermo-mechanical issues, was
For the first time a laser head for the generation a laser-water-jet for macro machining has been designed, built and
tested in a new high-power laser test rig with active laser safety at Fraunhofer IPT. In order to increase the transmittable
laser power the internal water supply was up-scaled to high flow rates and specialized high power optics as well as
suitable cooling strategies were developed to ensure increased thermal stability. Using a 30 kW fiber laser the new
machining head is tested and its thermal stability is investigated. The effects of system stability on the water-jet
properties are studied in order to identify further system improvement. Finally, possible applications for using the new
technology are outlined and first processing trials are performed.

Keywords: Laser-Water-Jet, High-Power, Laser Head Development, Macro Processin


Study of laser wobbling welding process through the radiation of plasma plume
Mrna, Libor; Horník, Petr; Jedlicka, Petr; Pavelka, Jan

During laser welding with wobbling to the vector of the welding speed adds trivial movement of the beam in the shape
of a circle or other shapes. Therefore, the laser beam moves with much higher current speeds than during normal
welding. The melting of material on the leading edge of the keyhole occurs periodically. This fact is reflected in the
character of the radiation of plasma plume over the keyhole. Experiments were conducted in which it was obtained
spectrum of plasma plume radiation by using autocorrelation function for different parameters of circular wobbling
(circle diameter, frequency) and for different materials. In the spectra are found the higher harmonic frequency of
wobbling. The results were also compared with the radiation of the plasma plume during pulsed laser welding where the
laser beam also periodically melts the leading edge.

Keywords: laser welding; wobbling; process monitoring


193 & 248 nm high power lasers for the micro and macro material processing
Fujimoto, Junichi; Kakizaki, Koji; Kobayashi, Masakazu; Oizumi, Hiroaki; Mimura, Toshio; Mizoguchi, Hakaru

Recently infrared laser has faced resolution limit of finer micromachining requirement on especially semiconductor
packaging like Fan-Out Wafer Level Package and Through Glass Via hole which are hard to process with less defect. In
this study, we investigated process capabilities with deep ultra violet excimer laser to explore its possibilities of
micromachining on organic and glass interposers. These results were observed with an optical microscopy and Scanning
Electron Microscope.
We have succeeded 9 micron meter holes on organic and 100 micron meter aspect ratio 5 on glass interposer without
any significant defects. As the ablation rates of both materials were quite affordable value, excimer laser is expected to
be put in practical use for mass production.

Keywords: excimer laser, 193nm, 248nm, KrF laser, ArF laser, material processing, micromachining


Process stability of laser induced plasma for hardness measurements
Czotscher, Tobias Markus; Vollertsen, Frank

Optical plasma position measurements are performed to establish a new hardness measurement method based on
laser-induced shockwaves. The process differs from conventional hardness measurements: Plasma is created with a
pulsed TEA-CO2 nanosecond laser on a material surface. Further interactions between the laser beam and plasma result
in a shockwave. The pressure of the shockwave can be used to push a test specimen inside a material surface. On the
one hand, plasma can be formed above the test specimen, which is then directly pushed inside the material surface. On
the other hand, the plasma can be created on an external target, and the shockwave then pushes the test specimen
inside the material. To increase the reproducibility of the laser-induced shockwave process, the influence of target
material is analysed. Aluminium alloy (EN AW 6082), hardened steel (100Cr2) and ceramic (Al2O3) are tested as target
materials. The geometry of the plasma and the position of the shockwave centre above the surface are detected to gain
further knowledge of the process. The experiments showed that the oxide ceramic target material shows the lowest
plasma geometry and shockwave pressure deviations and accordingly, the highest reproducibility, which makes it
suitable for further laser-induced hardness measurements.

Keywords: Process control; Material; Measurement


Twin Hexapod Operated Beam Expander and Dual Pyrocam Measurement for Laser Beam Path Optimization
Jamalieh, Murad Aziz George; Bohrer, Markus; Weinberger, Bernhard

Beam path optimization is a procedure in which beam parameters in terms of diameter and divergence are adjusted to
produce a beam that fits inside the intended beam delivery optics with a minimal obtained divergence along a defined
path length. In flatbed engraving and cutting machines working distances up to 6 m or even more are expected,
therefore a well collimated beam (i.e. propagates parallel) along this path distance is required for presentable clean
cutting or engraving results. The commercially available beam expanders used in beam path optimization are limited in
adjustability and usually not customized to certain laser devices. Lasers are manufactured with different parameters and
customized beam expanders would be the best solution. CO2 lasers are being used in this research. A laser beam
adjustment process will be researched using two robot translation stages (Hexapods) acting as two lens holders in
addition to a camera based laser beam profiler Pyrocam (capable of detecting 10600 nm wavelength), all mounted
inline on an extendible test bench (up to 12 m). The bench is one of its kind and used constantly for laser device testing
and evaluation. The optimization process uses algorithms to automatically drive the bench’s movable elements
constantly until the desired beam path parameters yield satisfactory results. The infrared camera is used to monitor the
adjusted (distorted) beam in comparison to a reference and during that the system analyses the beam parameters
(diameter and divergence). The robots will be periodically changing the position of the lenses to observe how lens tilting
and shifting affects the beam parameters.
After checking laser systems with beam expanders, significant deviation in beam size up to approx. 89% over 6 m was
calculated. With our method deviations in beam collimation and size will be dramatically improved across the engraving
distances resulting in a constant engraving quality.

Keywords: CO2 laser; beam expander; hexapod; Pyrocam; cutting; engraving


Laser scribing of alumina ceramics by Nd:YAG and ytterbium fiber laser
Rihakova, Lenka; Chmelickova, Hana

This paper focuses on laser scribing of alumina ceramics as they are hard to machine by conventional methods due to
their high hardness and brittleness. Scribing is very promising method of separation based on making a groove, either
fully penetrated or not. The scribed line creates a stress concentration and weakens the structure thus enabling easy
breakage of the material along the line using mechanical force. Scribing process and the depth of penetration depend on
laser parameters, laser beam diameter and its quality. The quality of the process is ensured by the less amount of debris
and heat affected zone and no evidence of cracking. In this paper laser scribing of alumina ceramics using Nd:YAG and
quasi-continuous-wave fiber laser was investigated in dependence on pulse length, pulse energy, pulse frequency, peak
power and number of crossings. Optimum combinations of process parameters to ensure good results and easy
breakage of samples using mechanical force were found for both lasers.

Keywords: alumina ceramics; laser scribing; groove characteristics


Time-resolved temperature measurement during laser marking of stainless steel
Kucera, Martin; Martan, Jirí

Laser marking is a well-established technology in industry; however there are still issues where the marking
process itself needs to be investigated. The surface microstructure and the phase composition can be
changed by the laser treatment. For this reason we present a study of temperatures reached by different
parameters of laser marking and their correlation with resulted microstructure and phase composition. The
marking was done using nanosecond pulsed fibre laser with variable pulse duration (from 9 to 200 ns),
repetition frequency and pulse energy. Similar marking was obtained by different parameters but different
phase composition and it correlates well with maximum temperatures reached in the laser spot, which
varied from less than 1100°C to more than 1800°C. From the results it can be concluded that combination of
longer pulse duration and higher repetition rate are the most suitable parameters for achieving the stainless
steel marking without surface melting.

Keywords: time resolved temperature measurement; laser; marking; stainless steel


Flexible, compact and picosecond laser capable four-beam interference setup
Peter, Alexander; Onuseit, Volkher; Faas, Sebastian; Freitag, Christian; Graf, Thomas

Periodic micro structures on surfaces offer unique properties, such as hydrophobic behavior, holographic light reflection
or friction and wear minimization. Multi-beam interference patterning is a technology to produce micro structures from
several micrometers down to below 1 μm, dependent on the wavelength and angle between the interfering beams. A
high power capable four-beam interference setup, designed for infrared ultrashort pulsed laser sources in the
picosecond regime will be shown. The setup provides independent variation of the period, intensity distribution and
pattern size of the interference pattern. The period is variable from 1 μm with a working distance of 100 mm up to 5 μm
with a working distance of about 800 mm. The intensity distribution can be modified to different shapes, such as lines,
holes, ripples etc. by controlling the polarization of each beam separately. The fluence of the pattern is controllable by
changing the pattern size. To change the pattern size, the beam diameter can be varied by a telescope with variable
focal length. The setup is built in a stable design of a size of about 300x300x300 mm³ and a weight of 4.6 kg. To avoid
aberrations at high laser power, especially focus shift, the setup was designed with high reflective mirrors. An
experimental verification shows the comparison between the experimental results and the calculated design and

Keywords: Direct Laser Interference Patterning; four beam interference; micro structuring; picosecond pulsed laser


Femtosecond processing with programmable spatial beams
Audourd, E.; Machinet, G.; Courjaud, A.; Hönniger, C.; Mottay, E.; Di Maio, Y.; Landon, S.; Dusser, B.

In the frame of the development of flexible micromachining workstations , spatial beam shaping appears to be a
significant improvement for femtosecond processes. An adequate phase function displayed on a phase modulator leads
to a custom intensity distribution in the Fourier plane of an objective lens, and consequently provides a customized laser
tool. Electrically addressed spatial light modula to rs (SLM) add flexibility and ease-of-use while maintaining a high spatial
resolution compatible. We present processing results obtained with an industrial tool coupling femtosecond lasers with
beam phase manipulation. Programmable spatial beamshaping contributes to increase the application range of
femtosecond processes by enlarging its field from direct surface processing of complex shapes and speeding processing

Keywords: femtosecond laser processing, spatial light modulator, parallel processing


Optical monitoring and control in laser additive technologies
Chivel, Yuri

Advanced methods and systems for monitoring and control of laser additive technological processes in real time are
designed and implemented. Precision control of the main physical parameters of these processes maximum surface
thermodynamic temperature , temperature distribution in the processing area, size of the melt and control their
evolution are necessary. Also control of quality and geometric dimensions of 3D object is implemented using 2D image

Keywords: laser additive technologies, optical monitoring and control, thermodynamic temperature, melt pool dimensions,
dimensions of 3D object ;


High energy and dual-pulse MOPA laser for selective recovery of non-ferrous metals
Lebour, Youcef; Juliachs, Jordi; Oriach, Carles

A high energy double-pass master oscillator power-amplifier system has been developed, in which the oscillator is a
passive Q-switch Nd3+:YAG/Cr4+:YAG microchip laser and the amplifier is a Nd3+:YAG laser crystal longitudinally-pumped
with a high-power diode. Laser pulses of ~1.5 ns duration in a TEM00 mode are generated from the microchip laser, while
their energy is increased up to 20 mJ by the power-amplifier. Moreover, the laser can be operated in single or dual-pulse
mode with an inter-pulse delay of ~ 50 ± 10 s; and with a repetition rate from single shot up to 100 Hz. The developed
laser device is aimed, but not limited, to selectively recover high value aluminium alloys from end-of-life vehicles waste,
by means of a Laser Induced Breakdown Spectroscopy technique. The unique characteristics of the laser provide
sufficient depth of field to accommodate scrap pieces of different heights (±2 cm), arriving at a velocity of 2 m/s and at
different angles (± 12°).

Keywords: Micro Processing; System Technology; MOPA laser system; Recycling; LIBS


Application of two-photon polymerization technique for resonator-based biosensors fabrication
Saetchnikov, Anton; Saetchnikov, Vladimir; Tcherniavskaia, Elina; Ostendorf, Andreas

An approach to produce resonator-based biosensors able to perform real-time biochemical component detection based
on spectral changes of whispering gallery modes by using two-photon polymerization is discussed. The main emphasis in
this paper has been made on the manufacturing of active resonators doped with CdSe/ZnS core-shell quantum dots
(QDs). Efficiency of direct introduction of active units and preprocessed QDs embedding techniques are compared.
Experimental data on detection of bovine serum albumin protein solution with active resonators is represented.

Keywords: Two-photon polymerization, biosensor, resonator, processing, quantum dot


Fast high yield cutting of 4 and 6 inch SiC-wafer using Thermal Laser Separation (TLS)
Belgardt, Christian; Kosuch, Reinhard; Lewke, Dirk; Grimm, Michael; Zühlke, Hans-Ulrich

TLS-Dicing™ is a kerf free laser based separation technology. After development of the basic principle [1] and the
demonstration of high separation quality [2] current work is focused on yield improvement. First we investigated the
influence of structures inside dicing street on the TLS process. Two different laser wavelengths were used to figure out
how to minimize the influence of metal structures, minimization of particles and reduction of heat affected zones on the
scribe process. The resulting parameters we applied on thin 4-inch SiC wafers and thick 6-inch SiC wafers. During this
work performance indicator values like yield, throughput and chip quality were determined. A very high geometrical
yield of more than 96 % could be verified. Finally, observed potential risks of yield loss are discussed and transferred into
design rules and best practice based dicing rules.

Keywords: laser dicing; SiC wafer; semiconductor production; kerf free


Laser-micro-processing with ultrashort pulses using flexible beam delivery
Jaeggi, B.; Neuenschwander, B.; Remund, S.; Eilzer, S.; Funck, M. C.; Wedel, Bjoern

Hollow core and kagome photonic crystal fibers offer the possibility to guide ultrashort laser pulses of high energy and
average power. They could represent a valuable tool for the power transport from the laser source to the processing
unit and would therefore facilitate the integration of ultrashort pulsed laser systems. Many works dealt with the
characterization of such fibers concerning beam quality, transmission, polarization etc. when the fiber is in a static
position. We combine such a fiber with a femtosecond laser system and our synchronized galvo scanner setup and
investigate the influence of a dynamic movement of the fiber. Beside the characterization of the output beam we also
demonstrate its influence onto the machining quality for the applications 3D-surface structuring and multi-pulse drilling
on the fly. Especially the latter application should be very sensitive to any variations of the beam pointing and
The experiments demonstrate the applicability of such fibers for its integration in an industrial environment for laser

Keywords: hollow core fiber; kagome fiber; static and dynamic mode; galvo scanner; laser-micro-machining


Simultaneous 3D laser processing with mechanical axes and galvanometric scanner
Flemmer, John Walter

The use of complex shaped 3D parts is a constantly increasing trend to meet modern functional or aesthetical demands.
At the same time, the demands on the machine kinematics are increasing with the complexity of the geometries and the
processing speed. For many laser based processes it is advantageous to rapidly guide the laser beam focus over the
surface with the use of galvanometric laser scanners with almost inertia-free axes. Due to the limited working volume
and the fixed beam direction of such devices they are often combined with mechanical axes. State of the art is the
sequentially processing of larger or curved surfaces in small tiles by using mechanical axes for successive repositioning.
This can lead to unwanted defects in the overlapping regions of the tiles (most relevant for laser polishing) and slows
down the overall processing speed (most relevant for laser micro structuring). A continuous processing where both
systems are moving at the same time solves this issues.
In this paper an approach for synchronizing the movements of a mechanical 5-axis system with a 3D laser scanner is presented. The approach doesn’t require further complex hardware because it mostly based on offline calculations. Furthermore experimental investigations on the accuracy of the overall system are presented. The final results show
that an accuracy of approximately 10 μm can be achieved with using the tested equipment.

Keywords: laser scanner; laser polishing; laser structuring; simultanous processing


Application of laser-spectroscopy on organic photovoltaic devices
Banerjee, Shyama Prasad; Sarnet, Thierry; Sentis, Marc; Kuntze, Thomas; Fledderus, Henri; Salem, Ahmed; Akkerman, Hylke; Friedrich-Schilling, Niels; Gburek, Benedikt; Anderson, Merve; Cros, Stéphane

Organic photovoltaics (OPV) with integrated ultra-barrier layer instead of afterward encapsulation are advantageous
due to combination of functionalities: substrate for layered stack generation and protection against lifetime-limiting
climatic exposure. Additionally, integration of the barrier into the functional layer stack saves one encapsulation step in
the production. European H2020 project ALABO (Advanced Laser Ablation on Barrier films for Organic and large area
electronic devices), addresses the challenges of lifetime enhancement and performance-cost-ratio . The consortium
includes 3 multi-national industries, 3 research institutes and 1 university from 4 European countries.
To include an ultra-barrier layer onto the plastic substrate with functional opto-electrical layers on top and qualification of a roll-to-toll (R2R) suitable production process, implies development of adequate coating, laser
structuring and characterization processes. Laser structuring of the front electrode (indium-tin-oxide ITO or dielectric-
metal-dielectric DMD; P1 scribing), the electric energy generating organic layer (P2 scribing) and the back electrode
layer (P3 scribing) are potentially harmful to the thin-film barrier underneath. Therefore, P1-P3 laser process
development goes hand-in-hand with barrier performance characterization and performed by water vapour
transmission rate (WVTR) measurements using tunable diode laser absorption spectroscopy (TDLAS), He-transmission-
test, in-house developed optical Ca-test and Hyper-spectral Imaging (HSI).
A real time diagnostic setup for selective ablation during laser scribing using laser-induced breakdown spectroscopy (LIBS) technique was investigated to obtain the material identification at every laser pulse. The paper presents results of
femtosecond and picoseconds LIBS, which generally enable discrimination of the separate laser-machined nm-scale
layers by their corresponding emission lines.

Keywords: Organic solar cell; Laser scribing; Process control; Selective ablation; Laser spectroscopy


Synthesis and resizing silver nanoparticles by laser ablation in liquids
Fernández, Mónica; del Val, Jesús; Boutinguiza, Mohamed; Riveiro, Antonio; Comesaña, Rafael; Lusquiños, Fernando; Pou, Juan

Silver nanoparticles are having great attention due to their remarkable optical, electrical and antimicrobial properties, which make them used in many different technological and scientific applications. In this work we present the results of obtaining silver nanoparticles by ablating a silver target submerged in de-ionized water. To resize and get uniform nanoparticles, subsequently laser ablation under different conditions was carried out onto the obtained colloidal solutions. The synthesis of nanoparticles has been carried out using a nanosecond Nd:YVO4 laser operating at 532 nm. The obtained particles are analyzed and the nanoparticles resizing mechanism is discussed. The obtained nanoparticles were characterized by means of transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS) and UV/VIS absorption spectroscopy. The obtained nanoparticles consisted in Ag particles with rounded shape. The size of particles has been reduced by subsequent laser irradiation to give smaller nanoparticles with narrow size distribution. However the irradiation lead to particles melting and formation of agglomerations.

Keywords: Silver nanoparticles; laser ablation, resizing